Education for Sustainable Development in Turkish Language Textbooks: A Multidimensional Analysis of Grade 5 and Grade 6 Textbooks Within the Türkiye Century Education Model

Abstract

Education for Sustainable Development (ESD) emphasises the integration of sustainability across subject areas, including language education. This study examines ESD representation in Grade 5 and Grade 6 Turkish language textbooks developed within the Türkiye Century Education Model (TYMM). Four textbooks comprising 12 themes were analysed through qualitative document analysis using eight Global Citizenship Education/Education for Sustainable Development (GCED/ESD) thematic areas and three ESD learning domains: cognitive, socio-emotional, and behavioural. Representation was coded as not represented (0), implicit (1), or explicit (2). Two researchers coded the corpus independently. Raw agreement between the coders was 78.47%, with a linearly weighted Cohen’s κ of 0.593. The thematic areas, however, were not represented to the same extent. Human Survival and Well-being was the most widely represented thematic area, followed by Cultural Diversity and Tolerance, Peace and Non-violence, and Human Rights. Climate Change, Gender Equality, and Sustainable Consumption and Production appeared less frequently across the themes. In terms of learning domains, cognitive and socio-emotional representation was equal, with each accounting for 36.4% of the total descriptive score; the behavioural domain accounted for the remaining 27.1%. Of the 78 domain-level decisions in which ESD was represented, 79.5% were explicit. Overall, the findings indicate the potential of mother-tongue language textbooks to provide opportunities for ESD, while highlighting areas for broader thematic coverage and more consistent behavioural engagement.

1. Introduction

Education for Sustainable Development (ESD) has become an important part of international efforts to provide learners with the knowledge, values, attitudes, skills, and capacities needed to help build more sustainable societies. Education is at the heart of this effort, as SDG 4.7 of the United Nations 2030 Agenda calls for learners to acquire the knowledge and skills required for sustainable development, particularly through ESD, human rights, gender equality, a culture of peace and non-violence, global citizenship, and appreciation of cultural diversity [1]. UNESCO’s ESD framework emphasises that education extends beyond knowledge acquisition to include cognitive, socio-emotional, and behavioural dimensions of learning [2,3]. Such a multidimensional understanding aligns with the broader competence-based framework of sustainability education. Within this broader framework, sustainability education foregrounds systems thinking, anticipatory thinking, normative and strategic competence, collaboration, critical reflection, and the ability to translate knowledge into action [4,5,6].

This transition from knowledge acquisition to multidimensional and action-oriented learning should also be reflected in educational materials in the field of sustainability. ESD is not limited to environmental issues but includes social, cultural, ethical, and economic concerns as well. Learners need opportunities not only to gain knowledge about these issues but also to reflect on values, participate, and take action [2,3]. Competence-oriented and transformative approaches make a similar connection between cognitive learning and affective, participatory, and action-related dimensions [7,8,9,10]. For this reason, simply identifying whether a sustainability-related topic is present in an educational material is not enough. How learners engage with the topic also needs to be considered. Such engagement is shaped not only by the content itself but also by the instructional context in which it is used.

Textbooks play an important role in this process because they carry curriculum content while also shaping many of the learning experiences provided to students. In terms of ESD, their contribution is not limited to providing information about sustainability. Sustainability-related questions, discussions, research, problem-solving activities, communicative tasks, and learner-generated work can all influence how students engage with sustainability issues. UNESCO MGIEP considers textbooks in core subjects, including language education, an important means of integrating sustainable development, peace, and global citizenship into mainstream education [11]. Previous research indicates that textbooks can create opportunities for conceptual understanding and action competence. However, the degree to which they provide such opportunities differs across educational materials [12,13].

In language education, such opportunities can emerge through the texts learners encounter and the activities they complete. Language textbooks are primarily designed for language learning, but the texts and activities they contain also bring students into contact with social, cultural, environmental, and ethical issues. Reading, listening/viewing, speaking, writing, interpretation, and discussion can give learners opportunities to encounter different perspectives, reflect on values, negotiate meaning, and express their own responses. Studies have examined ESD and the SDGs in English-language curricula and textbooks [14,15,16,17,18,19,20,21], as well as sustainability competencies and the ways sustainability issues are addressed through language-learning activities.

More specifically, language education can contribute to ESD by providing opportunities for learners to critically interpret sustainability-related messages, consider alternative perspectives, articulate reasoned positions, and communicate possible responses to social and environmental issues. Recent scholarship has emphasised the potential of language teaching to integrate sustainability-related competencies with communicative learning, critical reflection, and learner participation [18,19,21]. In mother-tongue education, these opportunities can be embedded in reading, writing, speaking, and listening activities that encourage students to examine issues, justify their views, and formulate responses. However, the inclusion of sustainability-related content does not necessarily indicate that such learning opportunities are meaningfully developed.

2. Literature Review

Previous research has examined the integration of ESD and sustainability-related themes into language education from different perspectives, including curriculum design, textbook content, and classroom learning opportunities. These studies provide a basis for understanding how sustainability is represented in educational materials and for identifying areas that require further investigation.

Mohammadnia and Moghadam [12] identified sustainability-related content in Iranian English-language textbooks, but found that it was unevenly distributed across the textbook series. Arslan and Curle [16] reported limited engagement with the SDGs in the Turkish high-school English curriculum, with ESD-related learning objectives mainly reflecting the cognitive dimension. Lasekan et al. [17] examined an EFL textbook from a broader perspective by considering not only its sustainability content but also the learning opportunities related to sustainability competencies. More recent studies have also reported differences in both the sustainability themes covered and the ways these themes are developed through language-learning materials [18,19,20]. The presence of sustainability-related content, therefore, does not necessarily reveal how that content is developed as part of the learning process.

In Türkiye, research on sustainability and language education has mostly focused on foreign-language teaching. In addition to the curriculum analysis conducted by Arslan and Curle [16], studies have examined EFL teachers’ perceptions of ESD [22], the representation of sustainability in Turkish secondary school English curricula and textbooks [23], pre-service ELT teachers’ lesson planning in relation to the SDGs [24], and the professional development needs of English-language teachers within the Türkiye Century Education Model (TYMM) [25]. This literature is relevant to the present study, but most of it comes from foreign-language education. Mother-tongue language education has distinct curricular aims, learner groups, and instructional practices and therefore needs to be considered in its own context. At Grades 5 and 6, Turkish language education aims to develop students’ listening/viewing, speaking, reading, and writing skills while strengthening their ability to understand, interpret, evaluate, and produce texts. These language practices also provide opportunities for students to express their views, engage with different perspectives, and develop awareness of social and cultural issues. Accordingly, examining sustainability-related learning opportunities in Turkish language textbooks is relevant not only to the content presented but also to the communicative and interpretive skills that the subject seeks to develop.

Research dealing specifically with sustainability in Turkish-language education is more limited. Ölçer and Öztürk [26] examined Grade 4 Turkish curricula and textbooks in relation to the SDGs, while Sosyal and Akbulut [27] analysed SDG representation in Grade 5 Turkish and Social Studies textbooks developed within TYMM. Sustainability has also been examined in materials used for teaching Turkish as a foreign language [28]. Although this work is closely related to the present study, the educational context is different. Turkish as a foreign language involves materials prepared for second- or foreign-language learners, whereas the present study deals with Turkish as a mother-tongue school subject. The two settings therefore differ in terms of their learners, curricular aims, and the way instruction is organised.

The introduction of TYMM has added a new dimension to research on sustainability in Turkish educational materials. The model brings knowledge and skills together with values, social-emotional learning, literacy, and the Erdem-Değer-Eylem framework in curriculum and textbook design [29]. Researchers have recently begun to examine how these components relate to sustainability. For instance, Bilen et al. [30] considered the Erdem-Değer-Eylem approach within the context of the SDGs and GreenComp. Other studies have focused on related aspects of TYMM textbooks, including values and social sustainability [31,32]. This is still an emerging area of research, particularly with regard to sustainability in Turkish-language textbooks developed within the new model.

Despite this growing literature, there is still a need to look more closely at how ESD is represented across complete instructional sequences in mother-tongue Turkish textbooks. Previous studies have identified sustainability themes, SDG representation, curricular objectives, and sustainability-related content in different textbook contexts [12,16,17,18,19,20,26,27,28,32]. Some recent research has also considered how sustainability is developed through the learning activities included in language materials [20]. Yet identifying a sustainability-related topic does not necessarily show whether the material provides opportunities for students to engage with it cognitively, socio-emotionally, behaviourally, or through more than one of these domains. The boundaries between related topics also need to be clearly defined. A reference to nature should not automatically be interpreted as Environmental Sustainability. Similarly, the presence of a female character is not in itself sufficient to identify Gender Equality. What remains less clear is how ESD thematic areas are represented across complete instructional sequences, how they relate to different ESD learning domains, and whether that representation is implicit or explicit.

To explore this issue, four Turkish language textbooks for Grades 5 and 6 developed within TYMM were examined. The analysis draws on eight Global Citizenship Education/Education for Sustainable Development (GCED/ESD) thematic areas identified in the metadata for SDG Indicator 4.7.1: Cultural Diversity and Tolerance, Gender Equality, Human Rights, Peace and Non-violence, Climate Change, Environmental Sustainability, Human Survival and Well-being, and Sustainable Consumption and Production [33]. These areas are considered together with UNESCO’s cognitive, socio-emotional, and behavioural ESD learning domains [2]. The analysis also considers whether ESD representation is absent, implicit, or explicit. Each textbook theme is treated as a complete instructional sequence rather than as a set of isolated passages or a count of sustainability-related terms. By bringing these dimensions together, the study examines thematic coverage, learning-domain representation, and the implicit–explicit distinction within the same analytical framework. This multidimensional approach makes it possible to examine not only where ESD appears in the textbooks, but also how it is pedagogically represented across complete instructional sequences. Accordingly, the study addresses the following research questions:

RQ1. Which GCED/ESD thematic areas appear in the Turkish language textbooks for Grades 5 and 6 developed within TYMM?

RQ2. Which cognitive, socio-emotional, and behavioural ESD learning domains are addressed through the GCED/ESD thematic areas represented in the textbooks?

RQ3. How is ESD represented across the analysed textbooks: implicitly, explicitly, or both?

RQ4. What similarities and differences can be identified between the Grade 5 and Grade 6 textbook corpora in terms of ESD representation?

3. Materials and Methods

3.1. Research Design

This study used qualitative document analysis to examine the representation of Education for Sustainable Development (ESD) in Grade 5 and Grade 6 Turkish language textbooks developed within the Türkiye Century Education Model (TYMM). The study involved the systematic identification, classification, and interpretation of sustainability-related learning opportunities in instructional materials, which made document analysis appropriate for the study [34].

The analysis went beyond searching for sustainability-related words or topics and reporting their frequencies. The inclusion of a potentially relevant concept alone was not considered evidence of ESD representation. Coding decisions took into account the instructional context in which the concept appeared, the nature of its connection to sustainability, how that connection was developed pedagogically, and the learning opportunity provided to students. This context-sensitive approach aligns with qualitative content analysis, in which textual material is examined systematically using a defined coding framework [35,36,37].

Two complementary dimensions formed the basis of the analytical framework. The first consisted of eight GCED/ESD thematic areas identified in the metadata for SDG Indicator 4.7.1: Cultural Diversity and Tolerance, Gender Equality, Human Rights, Peace and Non-violence, Climate Change, Environmental Sustainability, Human Survival and Well-being, and Sustainable Consumption and Production [33]. The second consisted of UNESCO’s three ESD learning domains: cognitive, socio-emotional, and behavioural [2]. Using these two dimensions together made it possible to examine both the sustainability areas represented in the textbooks and the forms of learner engagement associated with them.

3.2. Corpus and Selection of Textbooks

The study corpus comprised four Turkish language textbooks developed for Grades 5 and 6 within TYMM, with two textbooks analysed at each grade level [38,39,40,41]. Together, the four textbooks contained 12 themes: six in Grade 5 and six in Grade 6. The textbooks and themes included in the corpus are presented in Table 1.

Table 1. Corpus of the study.

Grade	Book	Themes Analysed	Number of Themes
Grade 5	Book 1	Game World; Getting to Know Atatürk; Recognising My Emotions	3
Grade 5	Book 2	Our Traditions; Communication and Social Relations; Healthy Living	3
Grade 6	Book 1	The Richness of Our Language; The Path to Independence; Different Worlds	3
Grade 6	Book 2	Communication and Social Relations; Science and Technology; Leader Spirits	3
Total	4 textbooks		12

The corpus was delimited according to the progressive implementation of TYMM and the availability of the corresponding Turkish language textbooks during the study period. All TYMM-aligned Turkish language textbooks available for Grades 5 and 6 within this period were included. Thus, the corpus represented the complete set of textbooks meeting the study’s inclusion criteria rather than a sample selected from a larger pool of eligible materials. Grade 7 was not included because the corresponding TYMM textbooks were not available during the study period. Accordingly, the corpus boundaries reflected the implementation stage of TYMM rather than a sampling procedure intended to represent all Turkish language textbooks.

The corpus was not intended to represent all Turkish language textbooks or all grade levels within TYMM. The analysis was restricted to the Grade 5 and Grade 6 textbook corpus defined by the scope and timeframe of the study.

3.3. Unit of Analysis

The main unit of analysis was the textbook theme. Clearly specifying the unit of analysis is important in systematic content analysis because coding decisions need to be applied to consistently defined units [36,37]. A theme was not treated as a collection of reading texts or unrelated activities. Instead, each theme was examined as a complete instructional sequence consisting of the different components through which language learning was organised.

Where present, these components included preparatory activities, reading texts, listening/viewing materials, comprehension and interpretation activities, language-related activities, speaking and writing activities, visual materials, research and discussion tasks, end-of-theme assessment activities, and production- or project-oriented tasks.

This approach was used because an ESD-related learning opportunity could develop across several components of the same theme. For example, a sustainability issue introduced in a reading or listening/viewing text could later be taken up through discussion, visual interpretation, speaking, writing, research, assessment, or production. However, the presence of a potentially relevant topic in one component alone did not qualify as ESD representation. The instructional framing within that component also had to meet the analytical criteria of the study. Examining the entire theme therefore made it possible to trace sustainability-related content across an instructional sequence while distinguishing meaningful ESD representation from incidental references.

3.4. Analytical Framework

The analytical framework had two complementary dimensions: a thematic dimension and a learning-domain dimension. The thematic dimension included eight GCED/ESD thematic areas identified in the metadata for SDG Indicator 4.7.1 [33], while the learning-domain dimension was based on UNESCO’s cognitive, socio-emotional, and behavioural domains of ESD learning [2]. The eight thematic areas and their operational focus are presented in Table 2.

Table 2. GCED/ESD thematic areas used in the analysis.

GCED/ESD Theme	Operational Focus in the Present Study
Cultural Diversity and Tolerance	Recognition, understanding, comparison, appreciation, or respectful engagement with cultural differences and commonalities
Gender Equality	Gender equality, equal opportunities, gender-related barriers or stereotypes, and meaningful representation of gender roles where pedagogically connected with equality
Human Rights	Rights, dignity, equality, inclusion, non-discrimination, justice, participation, citizenship, accessibility, or related rights-based issues
Peace and Non-violence	Peaceful coexistence, non-violence, constructive conflict resolution, reconciliation, and non-violent interpersonal or social problem solving
Climate Change	Explicit or clearly developed treatment of climate change, global warming, their causes, consequences, mitigation, adaptation, or related responses
Environmental Sustainability	Environmental responsibility, conservation, ecosystems, biodiversity, responsible interaction with nature, environmental degradation, or protection of natural environments
Human Survival and Well-being	Physical and mental health, emotional well-being, safety, resilience, healthy living, social well-being, and conditions supporting quality of life
Sustainable Consumption and Production	Responsible consumption, sustainable production, resource efficiency, waste reduction, reuse, recycling, sustainable resource use, or environmental consequences of production and consumption

Note: The eight thematic areas are based on the GCED/ESD themes identified in the metadata framework for SDG Indicator 4.7.1 [33].

The combined GCED/ESD framework adopted in this study reflects the broad scope of SDG Target 4.7, which encompasses environmental, social, cultural, and economic dimensions of sustainable development. Accordingly, ESD representation is used here in a multidimensional sense rather than as a synonym for environmental education. The eight thematic areas were retained as distinct analytical categories, allowing environmental concerns to be examined separately from, but alongside, issues such as human rights, cultural diversity, peace, and well-being. This distinction is important because a greater representation of social or cultural themes does not necessarily imply equivalent coverage of environmental sustainability.

The operational definitions were applied conservatively. For coding, conceptual or thematic similarity alone was not sufficient. There had to be a clear pedagogical link between the textbook content and the relevant ESD thematic area. This distinction was used to minimise overinterpretation and to distinguish substantive ESD representation from references to topics that might be related to ESD.

Human Survival and Well-being was operationalised as a multidimensional category encompassing physical, mental, emotional, and social well-being, as well as safety, resilience, healthy living, and quality of life. However, the presence of emotions, health-related vocabulary, or positive interpersonal interactions was not considered sufficient for assigning a non-zero code. Coding required a meaningful instructional connection to well-being, such as examining healthy practices, reflecting on emotional regulation, addressing social support, or considering responses to conditions affecting quality of life. This boundary was intended to distinguish substantive well-being-related learning opportunities from incidental references to everyday experiences.

3.5. Learning Domains

Each GCED/ESD thematic area identified within a textbook theme was assessed across all three learning domains: cognitive, socio-emotional, and behavioural. UNESCO [2] conceptualises these as interconnected dimensions of ESD learning. The cognitive domain concerns knowledge and thinking skills; the socio-emotional domain concerns values, attitudes, emotions, motivation, communication, collaboration, and self-reflection; and the behavioural domain concerns action and the capacity to act in relation to sustainability issues. The operational definitions and indicative evidence for the three learning domains are presented in Table 3.

Table 3. Operationalisation of the three ESD learning domains.

Domain	Operational Definition	Indicative Evidence
Cognitive	Opportunities to acquire, identify, explain, interpret, compare, analyse, evaluate, or apply knowledge related to an ESD issue	Information, explanation, comparison, causal relationships, problem identification, research, interpretation
Socio-emotional	Opportunities to engage with values, attitudes, emotions, empathy, responsibility, collaboration, perspective taking, belonging, motivation, or reflection related to an ESD issue	Empathy, value reflection, perspective taking, solidarity, emotional engagement, collaborative reflection
Behavioural	Opportunities to undertake, plan, select, propose, implement, or meaningfully simulate action directly related to an ESD issue	Decision making, solution development, action planning, application of sustainable practices, issue-related production or participation

The distinction between general student activity and behavioural ESD was particularly important because Turkish language textbooks contain many speaking, writing, research, presentation, and production activities. The presence of an activity or a requirement for student participation was not, by itself, considered evidence of behavioural ESD. To receive a behavioural code, the action undertaken, planned, proposed, or meaningfully simulated by the student had to be directly connected to the sustainability issue concerned. Thus, a generic writing, speaking, research, or presentation task was not coded as behavioural ESD simply because it involved active student participation.

For example, in the Grade 5 theme Our Traditions, Cultural Diversity and Tolerance received a behavioural code of 0 because the relevant activities did not require students to undertake an action directly related to this area. In Getting to Know Atatürk, Peace and Non-violence received a behavioural code of 1 because peace-related learning was present, but opportunities for action remained limited. By contrast, in Communication and Social Relations (Grade 5), Cultural Diversity and Tolerance received a behavioural code of 2 because students were asked to write a response email as part of an intercultural exchange activity involving an Azerbaijani student.

The use of these three learning domains was grounded in UNESCO’s framework for ESD learning objectives [2], while the eight GCED/ESD thematic areas were drawn from the metadata framework for SDG Indicator 4.7.1 [33]. In the present study, these two established frameworks were combined to examine not only which sustainability-related issues appeared in Turkish language textbooks but also how they were developed across different dimensions of learning. Applying this combined framework at the level of complete textbook themes made it possible to distinguish opportunities for knowledge development, socio-emotional engagement, and sustainability-related action within the same instructional sequence. The methodological contribution therefore lies in the systematic integration and operationalisation of existing frameworks for theme-level textbook analysis rather than in the development of a new ESD framework.

3.6. Coding Scale

Each combination of a GCED/ESD thematic area and learning domain within a textbook theme was coded using a three-level ordinal scale: 0 = not represented, 1 = implicitly represented, and 2 = explicitly represented. The coding criteria for the three levels are presented in Table 4.

Table 4. Coding criteria.

Code	Level	Operational Criterion
0	Not represented	No meaningful pedagogical relationship with the ESD theme/domain was identified.
1	Implicitly represented	A meaningful relationship with the relevant ESD thematic area could be identified from the instructional context, but the relationship was indirect, limited, or not fully developed within the learning domain.
2	Explicitly represented	The relevant ESD thematic area was directly addressed or clearly and substantively developed through the content and/or instructional task within the learning domain.

The difference between implicit and explicit representation was not based on whether particular terminology was used, but on the strength and pedagogical clarity of the relationship. The textbook did not need to use terms such as sustainability or ESD for a representation to be coded as explicit. A code of 2 could thus be given when the sustainability-related dimension was clearly and substantively developed, even without the use of sustainability-related terminology.

Conversely, the presence of words, images, topics, or concepts that could potentially be associated with sustainability did not by itself result in a code of 1 or 2. The instructional context had to support the corresponding ESD interpretation as well.

The 0–2 codes were not regarded as continuous psychometric measures, but as ordinal analytical categories indicating the level of representation within each thematic area–learning domain combination. For reporting purposes, each thematic area within a textbook theme could be expressed as a three-part profile in the order Cognitive/Socio-emotional/Behavioural. For instance, a profile of 2/2/1 indicated explicit cognitive representation, explicit socio-emotional representation, and implicit behavioural representation.

3.7. Coding Decision Rules

To minimise overinterpretation, boundary rules were created and applied during the coding process to maintain consistent conceptual distinctions within and across the four textbooks. These rules defined types of textbook content that were not, by themselves, considered sufficient evidence of one of the identified GCED/ESD thematic areas or learning domains. Table 5 summarises the boundary rules applied during coding.

Table 5. Boundary rules applied during coding.

Textbook Content	Not Automatically Coded as	Decision Principle
Cultural heritage, national history, traditions	Cultural Diversity and Tolerance	Evidence of cultural difference, comparison, commonality, intercultural engagement, or tolerance was required.
Nature, animals, landscapes	Environmental Sustainability	Environmental responsibility, conservation, ecological consequences, responsible interaction with nature, or protection of natural environments needed to be pedagogically developed.
Weather, seasons, rain, snow	Climate Change	Climate change, global warming, their causes or consequences, mitigation, adaptation, or a clearly established climate-related process was required.
Technology, innovation, products	Sustainable Consumption and Production	Sustainable resource use, waste reduction, reuse, recycling, responsible consumption, production impacts, or equivalent sustainability concerns were required.
Food or eating	Sustainable Consumption and Production	Health-oriented food content was considered in relation to Human Survival and Well-being unless sustainability-related dimensions of consumption or production were pedagogically developed.
Female figures or characters	Gender Equality	Female representation alone was insufficient; equality, equal opportunities, gender roles, stereotypes, barriers, or another pedagogically meaningful connection with gender equality was required.
War, national struggle, military conflict	Peace and Non-violence	Conflict itself was insufficient; peace, reconciliation, non-violence, peaceful coexistence, or constructive conflict resolution needed to be pedagogically developed.
Respect, kindness, positive relationships	Human Rights	A meaningful connection with rights, dignity, equality, inclusion, non-discrimination, justice, participation, citizenship, accessibility, or another rights-based issue was required.
Any writing, speaking, research, presentation, or production task	Behavioural learning	The action undertaken, planned, proposed, or meaningfully simulated by the student had to remain directly related to the corresponding ESD issue.

The boundary rules were applied consistently across textbooks and themes. Cultural heritage, for instance, was acknowledged as educationally important but did not necessarily equate with Cultural Diversity and Tolerance. Similarly, technological content was distinguished from Sustainable Consumption and Production, the presence of conflict from Peace and Non-violence, and general active-learning tasks from behavioural ESD. Hence, coding was based on the pedagogical framing and development of an issue rather than simply on surface similarity.

3.8. Coding Procedure

The analysis was carried out in several stages. Initially, the two researchers reviewed the whole textbook corpus and the analytical framework. Each textbook was organised by theme and instructional components to facilitate the use of the same analytical structure across the entire corpus.

Second, each of the 12 themes was analysed in the same way, using the same operational definitions, coding scale, and decision rules. The entire instructional sequence was considered rather than individual passages or activities in isolation. Potentially relevant evidence was analysed in its pedagogical context, including what students encountered and what they were expected to understand, reflect on, create, propose, or do. The use of a common coding framework and independent coding by two researchers supported a systematic and transparent coding process [35,37,42]. O’Connor and Joffe [42], in particular, discuss intercoder reliability in relation to systematicity, communicability, and transparency in qualitative coding.

Third, the two researchers independently assessed each of the eight GCED/ESD thematic areas across the cognitive, socio-emotional, and behavioural learning domains. Each thematic area–learning domain combination was coded as 0, 1, or 2. This resulted in 24 coding decisions for each textbook theme and 288 coding decisions for the 12-theme corpus (12 themes × 8 thematic areas × 3 learning domains).

Fourth, the two independent coding matrices were compared before any disagreements were discussed or resolved. The researchers agreed on 226 of the 288 coding decisions, resulting in a raw agreement of 78.47%. Since the coding scale was ordinal (0 = not represented, 1 = implicitly represented, 2 = explicitly represented), intercoder reliability was also assessed using linearly weighted Cohen’s kappa [43]. The calculated coefficient was κw = 0.593. Of the 62 initial coding disagreements, 29 occurred between codes 0 and 1, 17 between codes 0 and 2, and 16 between codes 1 and 2. Both raw agreement and weighted kappa were calculated from the initial independent coding rather than from the codes agreed upon later.

Once the reliability analysis was completed, the two researchers reviewed all coding disagreements together. They reconsidered each case using the relevant textbook evidence, operational definitions, coding criteria, and boundary rules specified for the study. Each disagreement was discussed until consensus was reached. The consensus codes formed the final coding matrix used for the descriptive analyses and reporting.

Finally, the final coding matrix was reviewed across the corpus to check that comparable evidence had been evaluated using the same coding criteria across textbooks, grade levels, and themes.

3.9. Data Analysis

The final consensus matrix was analysed descriptively at multiple levels. First, the ESD profile of each of the 12 textbook themes was examined at the theme level. The final cognitive, socio-emotional, and behavioural codes were reported for each of the eight GCED/ESD thematic areas within each theme.

Second, the final codes from the 12 themes were brought together to examine how the eight thematic areas were distributed across the corpus. For each GCED/ESD thematic area, cognitive, socio-emotional, and behavioural scores were summed separately, and a combined descriptive score was calculated by summing the three domain scores. The number of textbook themes in which each thematic area received at least one non-zero domain code was also recorded. This made it possible to distinguish between the breadth of themes in which an area appeared and its level of representation across the learning domains.

Finally, scores were combined across the learning domains to examine the relative distribution of cognitive, socio-emotional, and behavioural learning opportunities in the corpus. The frequencies of codes 0, 1, and 2 were also calculated to examine the overall distribution of absent, implicit, and explicit representation. In addition, Grade 5 and Grade 6 patterns were compared descriptively to identify similarities and differences in their ESD profiles.

All numerical summaries were used for descriptive rather than inferential purposes. Since the 0–2 codes indicated levels of representation, the numerical results were interpreted descriptively rather than as measurements on a continuous scale. The resulting totals and percentages were used to compare patterns across thematic areas, learning domains, textbook themes, and grade levels. No inferential statistical tests were conducted.

3.10. Trustworthiness and Analytical Rigor

Two international frameworks were used as the basis for the analysis. The eight thematic areas came from the GCED/ESD themes identified in the metadata for SDG Indicator 4.7.1 [33], while the cognitive, socio-emotional, and behavioural domains were based on UNESCO’s ESD framework [2]. These categories were used together with the operational definitions, coding criteria, and boundary rules described above. The boundary rules were especially useful when textbook content appeared to be related to ESD but did not provide enough evidence for a code. Comparable content was examined using the same criteria across textbooks and themes [35,36,37].

Independent coding allowed the researchers’ initial decisions to be compared before consensus was reached. Intercoder agreement was calculated at this stage, before any disagreements were discussed. In cases of disagreement, the researchers went back to the relevant evidence in the textbooks and re-examined each case using the predefined criteria and boundary rules. Final codes were therefore based on the instructional context in which the evidence appeared, whether in texts, listening/viewing materials, activities, questions, visuals, assessments, or production tasks. The final coding matrix, coding criteria and decision rules, and evidence supporting the final codes are provided in the Supplementary Materials.

4. Results

The results cover eight GCED/ESD thematic areas, 12 textbook themes, and the three ESD learning domains. The results are first presented by grade level and textbook, followed by cross-corpus analyses of thematic-area distribution, learning-domain distribution, levels of representation, and grade-level differences. In the theme-level tables, values are reported in the order Cognitive/Socio-emotional/Behavioural, where 0 indicates no representation, 1 implicit representation, and 2 explicit representation.

4.1. ESD Representation in Grade 5 Textbooks

The Grade 5 corpus consisted of six themes across two textbooks. ESD representation varied across thematic areas, learning domains, and textbook themes. The results for the two textbooks are presented separately below, followed by an overall summary of the Grade 5 pattern.

4.1.1. Grade 5, Book 1

Table 6 shows the ESD representation profiles across the three themes in Grade 5, Book 1.

Table 6. ESD representation in Grade 5, Book 1.

GCED/ESD Thematic Area	Game World	Getting to Know Atatürk	Recognising My Emotions
Environmental Sustainability	0/0/0	2/2/2	0/0/0
Climate Change	0/0/0	0/0/0	0/0/0
Sustainable Consumption and Production	0/0/0	1/0/0	0/0/0
Human Rights	2/2/1	0/0/0	0/0/0
Human Survival and Well-being	2/2/2	0/0/0	2/2/2
Cultural Diversity and Tolerance	0/0/0	0/0/0	0/0/0
Peace and Non-Violence	0/0/0	2/2/1	1/2/1
Gender Equality	0/0/0	0/0/0	0/0/0

Note: Values are presented as Cognitive/Socio-emotional/Behavioural. 0 = not represented; 1 = implicitly represented; 2 = explicitly represented.

In Grade 5, Book 1, ESD representation was concentrated in a limited number of thematic areas. Human Survival and Well-being was explicitly represented across all three learning domains in both Game World and Recognising My Emotions (2/2/2). Getting to Know Atatürk included explicit representation of Environmental Sustainability across all three domains (2/2/2), alongside Peace and Non-violence (2/2/1) and implicit cognitive representation of Sustainable Consumption and Production (1/0/0). Human Rights was also represented in Game World (2/2/1), while Peace and Non-violence appeared in Recognising My Emotions (1/2/1).

4.1.2. Grade 5, Book 2

Table 7 summarises the ESD representation profiles across the three themes in Grade 5, Book 2.

Table 7. ESD representation in Grade 5, Book 2.

GCED/ESD Thematic Area	Our Traditions	Communication and Social Relations	Healthy Living
Environmental Sustainability	0/0/0	0/0/0	2/2/2
Climate Change	0/0/0	0/0/0	0/0/0
Sustainable Consumption and Production	0/0/0	0/0/0	0/0/0
Human Rights	0/0/0	0/0/0	0/0/0
Human Survival and Well-being	0/0/0	2/2/2	2/2/2
Cultural Diversity and Tolerance	2/2/0	2/2/2	0/0/0
Peace and Non-Violence	0/0/0	2/2/2	0/0/0
Gender Equality	0/0/0	0/0/0	0/0/0

Note: Values are presented as Cognitive/Socio-emotional/Behavioural. 0 = not represented; 1 = implicitly represented; 2 = explicitly represented.

In Grade 5, Book 2, Our Traditions represented only Cultural Diversity and Tolerance (2/2/0), whereas Communication and Social Relations included Cultural Diversity and Tolerance, Peace and Non-violence, and Human Survival and Well-being, each explicitly represented across all three learning domains (2/2/2). In Healthy Living, Environmental Sustainability and Human Survival and Well-being were both explicitly represented across all three domains (2/2/2).

4.1.3. Overall Grade 5 Pattern

Across the six Grade 5 themes, Human Survival and Well-being was represented in four themes, followed by Peace and Non-violence in three. Environmental Sustainability and Cultural Diversity and Tolerance were each represented in two themes, while Human Rights and Sustainable Consumption and Production were each represented in one. Neither Climate Change nor Gender Equality was represented in the Grade 5 corpus.

Not all thematic areas represented in Grade 5 included a behavioural component. Several thematic areas were represented explicitly across all three learning domains (2/2/2), while others showed implicit behavioural representation or no behavioural representation.

4.2. ESD Representation in Grade 6 Textbooks

The Grade 6 corpus included six themes in two textbooks. All eight GCED/ESD thematic areas were represented at least once across these themes, although their distribution differed between the two textbooks. The following sections present the results for each textbook before considering the overall Grade 6 pattern.

4.2.1. Grade 6, Book 1

The ESD representation profiles across the three themes in Grade 6, Book 1 are reported in Table 8.

Table 8. ESD representation in Grade 6, Book 1.

GCED/ESD Thematic Area	The Richness of Our Language	The Path to Independence	Different Worlds
Environmental Sustainability	0/0/0	0/0/0	0/0/0
Climate Change	0/0/0	0/0/0	2/1/0
Sustainable Consumption and Production	0/0/0	0/0/0	0/0/0
Human Rights	0/0/0	0/0/0	2/2/1
Human Survival and Well-being	0/0/0	0/0/0	0/0/0
Cultural Diversity and Tolerance	2/2/2	2/2/1	2/2/2
Peace and Non-Violence	0/0/0	0/0/0	1/2/0
Gender Equality	0/0/0	1/1/0	0/0/0

Note: Values are presented as Cognitive/Socio-emotional/Behavioural. 0 = not represented; 1 = implicitly represented; 2 = explicitly represented.

In Grade 6, Book 1, Cultural Diversity and Tolerance was represented in all three themes, with profiles of 2/2/2 in The Richness of Our Language and Different Worlds and 2/2/1 in The Path to Independence. Gender Equality was implicitly represented in the cognitive and socio-emotional domains in The Path to Independence (1/1/0). Different Worlds showed the broadest ESD representation in the book, additionally including Human Rights (2/2/1), Peace and Non-violence (1/2/0), and Climate Change (2/1/0).

4.2.2. Grade 6, Book 2

Table 9 provides the ESD representation profiles across the three themes in Grade 6, Book 2.

Table 9. ESD representation in Grade 6, Book 2.

GCED/ESD Thematic Area	Communication and Social Relations	Science and Technology	Leader Spirits
Environmental Sustainability	0/0/0	2/2/2	0/0/0
Climate Change	0/0/0	0/0/0	0/0/0
Sustainable Consumption and Production	0/0/0	2/2/2	0/0/0
Human Rights	0/0/0	2/1/1	2/2/2
Human Survival and Well-being	2/2/2	0/0/0	1/2/1
Cultural Diversity and Tolerance	0/0/0	0/0/0	0/0/0
Peace and Non-Violence	2/2/2	0/0/0	0/0/0
Gender Equality	0/0/0	0/0/0	2/2/1

Note: Values are presented as Cognitive/Socio-emotional/Behavioural. 0 = not represented; 1 = implicitly represented; 2 = explicitly represented.

In Grade 6, Book 2, Communication and Social Relations represented Peace and Non-violence and Human Survival and Well-being across all three domains (2/2/2). Science and Technology included explicit representation of Environmental Sustainability and Sustainable Consumption and Production across all three domains (2/2/2), together with Human Rights (2/1/1). Leader Spirits included Human Rights (2/2/2), Gender Equality (2/2/1), and Human Survival and Well-being (1/2/1).

4.2.3. Overall Grade 6 Pattern

Cultural Diversity and Tolerance and Human Rights were each represented in three of the six Grade 6 themes. Gender Equality, Peace and Non-violence, and Human Survival and Well-being were each represented in two themes. Environmental Sustainability, Climate Change, and Sustainable Consumption and Production were each represented in one theme.

Thematic areas were also not equally distributed in the two Grade 6 textbooks. Cultural Diversity and Tolerance appeared in all three themes in Book 1 but was not represented in Book 2. In contrast, Environmental Sustainability, Sustainable Consumption and Production, and Human Survival and Well-being appeared only in Book 2. Climate Change occurred only in Different Worlds in Book 1.

4.3. Cross-Grade Comparison of ESD Representation

The Grade 5 and Grade 6 corpora differed in the number of themes in which individual ESD areas were represented and in the distribution of these areas across the two grade levels. Table 10 summarises the cross-grade distribution of the eight GCED/ESD thematic areas.

Table 10. Comparison of ESD representation by grade level.

GCED/ESD Thematic Area	Grade 5: Themes Represented	Grade 6: Themes Represented	Total
Environmental Sustainability	2/6	1/6	3/12
Climate Change	0/6	1/6	1/12
Sustainable Consumption and Production	1/6	1/6	2/12
Human Rights	1/6	3/6	4/12
Human Survival and Well-being	4/6	2/6	6/12
Cultural Diversity and Tolerance	2/6	3/6	5/12
Peace and Non-Violence	3/6	2/6	5/12
Gender Equality	0/6	2/6	2/12

Note: A thematic area was counted as represented in a textbook theme when at least one of its three learning-domain codes was non-zero.

Human Survival and Well-being was represented more frequently in Grade 5 (4/6 themes) than in Grade 6 (2/6), as were Peace and Non-violence (3/6 vs. 2/6) and Environmental Sustainability (2/6 vs. 1/6). In contrast, Human Rights (1/6 vs. 3/6) and Cultural Diversity and Tolerance (2/6 vs. 3/6) were more frequently represented in Grade 6. Gender Equality and Climate Change occurred only in Grade 6, whereas Sustainable Consumption and Production appeared in one theme at each grade level.

The summed descriptive coding scores were 67 for Grade 5 and 73 for Grade 6, and no inferential comparison was made between these scores.

4.4. Distribution of GCED/ESD Thematic Areas Across the Corpus

The eight GCED/ESD thematic areas differed in their distribution across the 12 textbook themes. Table 11 shows the distribution of coding scores across the three learning domains for each GCED/ESD thematic area.

Table 11. Distribution of GCED/ESD thematic areas across the 12 themes.

GCED/ESD Thematic Area	Cognitive	Socio-Emotional	Behavioural	Combined Score	Themes Represented
Human Survival and Well-being	11	12	11	34	6/12
Cultural Diversity and Tolerance	10	10	7	27	5/12
Peace and Non-Violence	8	10	6	24	5/12
Human Rights	8	7	5	20	4/12
Environmental Sustainability	6	6	6	18	3/12
Gender Equality	3	3	1	7	2/12
Sustainable Consumption and Production	3	2	2	7	2/12
Climate Change	2	1	0	3	1/12

Note: Domain scores are sums of the final 0–2 codes across the 12 textbook themes. The combined score is the sum of the cognitive, socio-emotional, and behavioural scores. A thematic area was counted as represented in a theme when at least one of its three learning-domain codes was non-zero.

Human Survival and Well-being had the highest combined descriptive score (34) and appeared in six of the 12 themes. Cultural Diversity and Tolerance and Peace and Non-violence were each found in five themes, with combined scores of 27 and 24, respectively. Human Rights appeared in four themes and had a combined score of 20.

Environmental Sustainability appeared in three themes and had a combined score of 18. Its cognitive, socio-emotional, and behavioural scores were equal (6/6/6). Gender Equality and Sustainable Consumption and Production each had a combined score of 7 and appeared in two themes. Climate Change appeared in one theme and had a combined score of 3.

4.5. Distribution Across Cognitive, Socio-Emotional, and Behavioural Learning Domains

The cognitive, socio-emotional, and behavioural scores together totalled 140. The overall distribution of coding scores across the three learning domains is presented in Table 12.

Table 12. Overall distribution of ESD learning domains.

Learning Domain	Total Score	Percentage of Total Score
Cognitive	51	36.4%
Socio-emotional	51	36.4%
Behavioural	38	27.1%
Total	140	99.9%

Note: Percentages refer to the coded representation in the corpus, not to measured student learning outcomes. Percentages may not total exactly 100% because of rounding.

The cognitive and socio-emotional domains had identical total scores (51; 36.4% each), compared with 38 (27.1%) for the behavioural domain. This distribution indicates that knowledge-related and socio-emotional learning opportunities received equal cumulative representation in the analysed textbooks. Although behavioural representation was comparatively lower, it accounted for more than one-quarter of the total descriptive score. The difference suggests that opportunities involving sustainability-related action were less extensively represented than those involving knowledge, values, attitudes, and reflection. These findings describe the relative distribution of coded learning opportunities within the corpus and should not be interpreted as evidence of students’ actual learning or behaviour.

4.6. Implicit and Explicit Representation of ESD

The corpus was examined for both implicit and explicit representation of ESD. There were 288 coding decisions in total, based on the 12 themes, eight GCED/ESD thematic areas, and three learning domains.

Of the 288 coding decisions, 210 (72.9%) were coded as not represented (0). The remaining 78 decisions (27.1%) indicated either implicit or explicit representation. Of these 78 non-zero codes, 16 (20.5%) were implicit and 62 (79.5%) were explicit. Table 13 summarises the distribution of coding levels across the corpus. When examined by learning domain, the cognitive domain included 5 implicit and 23 explicit codes, the socio-emotional domain included 3 implicit and 24 explicit codes, and the behavioural domain included 8 implicit and 15 explicit codes. Notably, half of all implicit codes occurred in the behavioural domain, indicating that behavioural learning opportunities were more often indirectly represented than those in the other two domains.

Table 13. Distribution of coding levels across the corpus.

Coding Level	Number of Domain-Level Codes	Percentage of All 288 Coding Decisions	Percentage of Non-Zero Codes
Not represented (0)	210	72.9%	—
Implicitly represented (1)	16	5.6%	20.5%
Explicitly represented (2)	62	21.5%	79.5%
Total	288	100.0%	—

Note: Percentages in the final column are based on the 78 non-zero coding decisions. Percentages may not total exactly 100% because of rounding.

Among the domain-level codes in which ESD was represented, explicit codes were more frequent than implicit codes (79.5% vs. 20.5%). However, these proportions need to be considered alongside the 210 zero codes, which accounted for 72.9% of all 288 coding decisions. This indicates that ESD representation was concentrated in a limited number of thematic area–learning domain combinations rather than distributed throughout the coding matrix. Where representation was identified, it was generally direct and substantively developed within the instructional context. Thus, the predominance of explicit codes among non-zero decisions should not be interpreted as evidence of comprehensive ESD coverage across the textbooks.

5. Discussion

The present study examined how Education for Sustainable Development (ESD) is represented in Grade 5 and Grade 6 Turkish language textbooks developed within the Türkiye Century Education Model (TYMM). Four key findings were identified. First, ESD representation was uneven across the eight GCED/ESD thematic areas. Human Survival and Well-being appeared in more themes than the other areas. Cultural Diversity and Tolerance, Peace and Non-violence, and Human Rights were also prominent in the corpus, while Climate Change, Gender Equality, and Sustainable Consumption and Production occurred less frequently. Second, cognitive and socio-emotional representation was equal at the corpus level, while behavioural representation was lower. Third, ESD was absent from many thematic area–learning domain combinations, but when representation occurred, it was predominantly explicit. Fourth, the two grade levels differed in the ESD areas represented, although their summed descriptive scores were relatively close (67 for Grade 5 and 73 for Grade 6). These findings are discussed below in relation to the thematic coverage of ESD, its distribution across learning domains, the distinction between implicit and explicit representation, and differences between the two grade levels.

5.1. Uneven Distribution of ESD Across Thematic Areas

Human Survival and Well-being had the highest combined score and was found in 6 of the 12 themes. Cultural Diversity and Tolerance and Peace and Non-violence each appeared in five themes, and Human Rights in four. For the remaining areas, frequencies were lower. This pattern could be read in the context of SDG Target 4.7, which brings sustainable development together with human rights, gender equality, peace and non-violence, global citizenship, and cultural diversity [1]. Social and well-being-related aspects were therefore more prominent in the analysed Turkish language textbooks than several of the less frequently represented areas, particularly Climate Change, Gender Equality, and Sustainable Consumption and Production.

This pattern should be interpreted in light of the broad GCED/ESD framework used in the study. The prominence of social and cultural areas is consistent with the multidimensional scope of ESD and should not be regarded as a departure from sustainability education. Nevertheless, the comparatively limited representation of Climate Change, Environmental Sustainability, and Sustainable Consumption and Production indicates that environmental and resource-related issues received less thematic coverage than several social and cultural concerns. The findings therefore suggest an imbalance in the distribution of sustainability-related learning opportunities rather than an absence of ESD. They also point to the potential value of extending environmental and resource-related learning opportunities within future Turkish language textbook activities.

An uneven distribution of sustainability content has also been reported in language textbooks from other contexts. Mohammadnia and Moghadam [12] identified sustainability themes in Iranian English-language textbooks but noted that their distribution across the series was not balanced. Sachdev and Vibulphol [18] reported a similar selectivity in a Grade 12 English textbook in Thailand. Environmental management and social justice were included, whereas essential human needs and infrastructure were not. A related pattern was found in the Turkish textbooks. However, these similarities should be interpreted cautiously because the studies differ in educational level, language-learning context, textbook corpus, and analytical framework. The present study additionally examines how sustainability themes are represented across cognitive, socio-emotional, and behavioural learning domains.

ESD content was present, but some thematic areas received much more attention than others. Similar unevenness has been reported in previous textbook research, which has highlighted the need for a more balanced distribution of sustainability themes across instructional materials [12].

The less frequently represented areas are particularly noteworthy. Climate Change appeared in only 1 of the 12 themes, while Gender Equality and Sustainable Consumption and Production each appeared in two. Environmental Sustainability was found in three themes. Huang [21] examined sustainability in a German-as-a-Foreign-Language textbook used in Chinese higher education, while Maijala, Patzelt, and Delius [20] investigated sustainability content in German-language coursebooks used in several European countries. These studies are relevant because they also examine how sustainability is addressed in language-learning materials, providing a broader context for interpreting the selective thematic coverage identified in the present study. However, differences in educational level, language-learning context, and analytical approach mean that their findings cannot be compared directly with the Grade 5 and Grade 6 Turkish textbooks examined here.

Theme frequency, however, was only one part of the picture. Sustainable Consumption and Production occurred in only two themes, but in Science and Technology it was explicit in all three learning domains (2/2/2). Environmental Sustainability occurred in three themes and had equal cognitive, socio-emotional, and behavioural scores (6/6/6). These examples show that occurrence and domain coverage are not the same: an area may appear in only a few themes but still extend across all three learning domains. The number of themes in which an area appeared and its representation across the three learning domains therefore provide different information about its place in the textbooks.

The prominence of Human Survival and Well-being should also be considered in relation to its relatively broad operational scope, which encompasses several dimensions of personal and social well-being. Although non-zero codes required meaningful instructional evidence, the breadth of this category may have contributed to its comparatively frequent representation.

5.2. Learning Domains: Beyond a Predominantly Cognitive Model

The findings also revealed differences across the three ESD learning domains. Cognitive and socio-emotional representation each accounted for 36.4% of the total descriptive score, while the behavioural domain accounted for 27.1%. The textbooks therefore did not show a predominantly cognitive pattern. Knowledge-related content was accompanied by socio-emotional opportunities involving values, attitudes, emotions, empathy, perspective taking, responsibility, collaboration, and reflection.

This differs from the pattern reported by Arslan and Curle [16] in their analysis of the Turkish high-school English curriculum, where ESD-related learning objectives were mainly cognitive and the socio-emotional and behavioural dimensions received less attention. In the present study, cognitive and socio-emotional representation had the same cumulative score. The difference may partly relate to what was included in the analysis. Rather than examining formal learning objectives alone, this study considered complete instructional sequences, including reading and listening/viewing texts, comprehension and interpretation tasks, speaking and writing activities, research and discussion tasks, assessment, and production tasks. Socio-emotional representation could thus be identified not only in explicitly stated learning outcomes but also in different parts of a theme. This methodological distinction is important when interpreting the difference between the two studies, as the distribution of learning domains may vary depending on whether the analysis focuses on curriculum objectives or the instructional opportunities presented in textbooks. Accordingly, the findings should be understood as evidence of a different pattern within the present corpus rather than as a direct indication of differences between mother-tongue and foreign-language education.

Behavioural representation was lower than cognitive and socio-emotional representation, although it was not absent. Behavioural codes occurred in several thematic areas and textbook themes. These codes were used when learners were asked to carry out, plan, propose, or meaningfully simulate an action related to a sustainability issue. The lower behavioural score therefore reflects fewer such action-oriented opportunities in the corpus rather than their complete absence.

Language activities are important in this regard. Lasekan et al. [17], in their analysis of an EFL textbook, considered how language-learning materials could contribute to sustainability awareness and sustainability competencies. This brings attention not only to the presence of sustainability content but also to what learners are asked to do with that content. The present findings add a mother-tongue language education context to this discussion. In the Turkish textbooks analysed here, some ESD-related opportunities occurred through communicative and productive language activities rather than through sustainability content alone.

Behavioural engagement in a language textbook may also differ from action in other curricular areas. In this study, a language activity received a behavioural code only when learners were expected to carry out, plan, propose, or meaningfully simulate an action directly related to the sustainability issue being addressed. For example, producing language in a speaking or writing activity was not, by itself, classified as behavioural. When communication formed part of a sustainability-related action, however, it could provide a form of behavioural engagement within language education. The action-oriented dimension of ESD can therefore be maintained even when the form of action differs across school subjects.

5.3. Selective but Predominantly Explicit Representation

A large part of the coding matrix consisted of zero codes. Of the 288 domain-level decisions, 210 received a zero code. There were 78 non-zero codes, of which 62 were explicit and 16 implicit. In percentage terms, explicit codes made up 79.5% of the cases in which ESD was identified. Thus, ESD did not occur across much of the matrix, but where it was found, it was usually clearly represented.

The high number of zero codes is also related to the coding criteria used in the study. Coding required more than a general association with sustainability. Nature and animals, for example, did not automatically count as Environmental Sustainability. Female characters or figures were not enough for Gender Equality, just as references to technology were not enough for Sustainable Consumption and Production. The activity or content had to address the relevant ESD area in a way that met the coding criteria.

This point is useful in interpreting the 210 zero codes. Textbook content could deal with social or environmental matters and still receive a zero if there was not enough evidence to assign it to one of the ESD areas. In other words, the zero codes refer to the criteria used for ESD representation rather than to the complete absence of socially or environmentally relevant material. This also helps explain the combination of many zero codes and a high percentage of explicit codes among the cases where ESD was identified. A loose thematic association was not considered evidence of ESD representation.

The results can also be viewed at more than one level. The number of themes in which an ESD area occurred shows how widely it was distributed, whereas the domain codes show what happened within those occurrences. The two did not always follow the same pattern. An area could occur in only a few themes and still involve cognitive, socio-emotional, and behavioural representation. In other cases, an area appeared in several themes without the same coverage across all three learning domains. This distinction is relevant to the implicit–explicit findings as well: the frequency of an ESD area does not by itself indicate whether its representation is implicit or explicit, or how many learning domains are involved.

5.4. Grade-Level Variation and Curricular Distribution

Grade 5 and Grade 6 had relatively close summed descriptive scores, 67 and 73 respectively, but the distribution of ESD areas was different. Human Survival and Well-being appeared in four Grade 5 themes and two Grade 6 themes, while Peace and Non-violence appeared in three and two themes, respectively. The opposite pattern was found for Human Rights, which appeared in one Grade 5 theme and three Grade 6 themes. Cultural Diversity and Tolerance was represented in two Grade 5 themes and three Grade 6 themes. Gender Equality and Climate Change appeared only in Grade 6.

Grade 6 did not simply contain more of every ESD area. Some areas were more common in Grade 6, while others were more frequent in Grade 5. Sustainable Consumption and Production, for example, occurred in one theme at each grade level. The main difference between the two grades was therefore in thematic emphasis rather than in their summed descriptive scores. The findings do not show a steady increase in ESD representation from Grade 5 to Grade 6.

The close summed scores also need to be considered in terms of what the coding system measures. The scores reflect the representation found in the textbooks, not curriculum quality, instructional effectiveness, or student achievement. The higher Grade 6 score should not be interpreted as evidence of higher curriculum quality. The two grades instead show different patterns in which particular ESD areas receive different levels of attention.

5.5. Implications for Mother-Tongue Language Education

The findings point to several ways in which ESD can become part of mother-tongue language education. Language textbooks provide content for learners to read, listen to, interpret, discuss, and produce. Sustainability issues can therefore enter language lessons through practices that are already part of the subject, including reading, listening/viewing, speaking, writing, discussion, interpretation, and text production.

Research in foreign-language education has also considered language textbooks as resources for sustainability learning. Mohammadnia and Moghadam [12] discuss the potential of English textbooks for ESD, while Sachdev and Vibulphol [18] examine the inclusion of sustainability-related content in language-learning materials. Maijala et al. [20] draw attention to both the sustainability content presented in coursebooks and the activities through which learners engage with that content. The present study brings a mother-tongue perspective to this discussion. In the Turkish textbooks examined here, ESD was found not only in texts dealing with sustainability-related issues but also in the activities surrounding those texts.

The concept of sustainability need not be separate from the typical work of a language class. In the corpus, some ESD areas were represented across the cognitive, socio-emotional, and behavioural domains within the same instructional sequence. A sustainability issue could become material for understanding and interpretation, reflection on values or perspectives, discussion, writing, and, in some cases, action-oriented language use. These are language-learning practices in their own right, rather than activities that need to be added separately to the subject.

The findings also identify two areas for further consideration in future textbook development. One concerns thematic coverage. Climate Change, Gender Equality, and Sustainable Consumption and Production appeared in relatively few themes in the corpus. The other concerns the behavioural domain, which had a lower descriptive score than the cognitive and socio-emotional domains. Behavioural opportunities could be developed through tasks in which learners formulate responses, discuss possible solutions, consider different perspectives, or produce texts for a sustainability-related purpose. Such tasks would still need to meet the behavioural criterion used in this study: language production alone would not be sufficient unless it formed part of an action related to the sustainability issue. This distinction is particularly relevant to the Türkiye Century Education Model’s emphasis on sustainability literacy and the translation of values into action. The findings suggest that future Turkish language textbooks could strengthen this connection by providing more opportunities for students to apply sustainability-related understanding and values through purposeful, action-oriented communication tasks. Concrete examples include drafting a school waste-reduction proposal based on a classroom audit, preparing a persuasive message advocating inclusive access to shared spaces, or developing a short public-awareness campaign on climate-related choices. In each case, students would use speaking or writing to propose a feasible response to a specific sustainability issue rather than merely describe the issue.

This does not imply that textbooks simply need a greater number of sustainability references. The results showed that thematic frequency and representation across learning domains provide different information. In mother-tongue language education, what also matters is how a sustainability issue relates to the language work learners are asked to undertake. Reading, interpretation, discussion, speaking, and writing can provide different ways of engaging with an issue. Creative activities can further enrich such engagement in sustainability-oriented learning [44], while action-oriented tasks can extend it when appropriate to the instructional context.

Within the Turkish educational context, these findings may inform the continued development and implementation of TYMM-aligned Turkish language textbooks. For textbook authors and curriculum developers, the results suggest that greater attention could be given to the distribution of GCED/ESD thematic areas and to the opportunities provided across different learning domains. For teachers, the findings highlight the potential to extend existing reading, discussion, and writing activities towards sustainability-related reflection and purposeful communication without moving beyond the central objectives of mother-tongue language education. However, the extent to which these opportunities are taken up in classrooms would depend on instructional practices and implementation conditions, which were not examined in the present study.

5.6. Methodological Contribution and Scope of Interpretation

The study combines three elements in its analysis of ESD in textbooks: thematic areas, learning domains, and the level of representation. Studies of language textbooks have approached sustainability from different angles, including sustainability themes and SDG representation [12,16,17,18,19]. Huang [21], for example, also considers how sustainability is handled pedagogically in language-learning material. In this study, these concerns were analysed within the same coding system. For each textbook theme, the analysis considered which GCED/ESD areas were present, whether they involved cognitive, socio-emotional, or behavioural learning, and whether the representation was implicit or explicit.

The unit of analysis also influenced what could be seen in the textbooks. A sustainability issue was not necessarily confined to a single text or activity. It might occur in a reading text and then continue in the questions that followed, or move into discussion, writing, research, assessment, or a production activity. For this reason, each textbook theme was treated as a complete instructional sequence. This made it possible to follow links between different parts of a theme during coding. It was also useful in cases where a text seemed close to a sustainability topic but the activities around it provided either further evidence for an ESD code or no such evidence.

There are definite limits to what these codes can tell us. They refer to the material provided in the textbooks rather than to what teachers and learners actually do with it. A behavioural code, for example, identifies an opportunity for action-oriented engagement in the textbook. It does not show that students took that action or developed a sustainability competence as a result. The reverse also needs to be considered. If an ESD area was absent from a particular theme, a teacher could still introduce it in the classroom. Classroom implementation, instructional effectiveness, and student learning are therefore outside the scope of this study.

The three parts of the framework also need to be kept separate when interpreting the results. Theme frequency indicates how widely an ESD area occurs across the corpus. The learning-domain codes provide information about its cognitive, socio-emotional, and behavioural representation. The implicit–explicit distinction concerns another aspect: how directly the area is represented. These measures provide different kinds of information. An area that occurs in only a few themes, for example, may still extend across all three learning domains. Likewise, frequent occurrence does not indicate whether the representation is implicit or explicit. Combining these dimensions offers a more detailed picture of where ESD appears in the textbooks and how it is represented.

6. Conclusions

This study examined ESD representation in Grade 5 and Grade 6 Turkish language textbooks developed within the Türkiye Century Education Model (TYMM). ESD was present in the four textbooks, although not to the same extent across the eight GCED/ESD thematic areas. Human Survival and Well-being appeared in more themes than the other areas, followed by Cultural Diversity and Tolerance, Peace and Non-violence, and Human Rights. Climate Change, Gender Equality, and Sustainable Consumption and Production were less frequent. The corpus, therefore, cannot be simply characterized by the presence or absence of ESD. Its representation was concentrated in particular areas and themes.

Variation was also found across the learning domains. The cognitive and socio-emotional domains each comprised 36.4% of the total descriptive score, with the behavioural domain comprising 27.1%. At the same time, many of the possible thematic area–learning domain combinations received a zero code. Where ESD was identified, however, explicit representation was much more common: 62 of the 78 non-zero codes (79.5%) were explicit. All of these findings need to be considered together. The number of themes in which an ESD area is present does not necessarily reflect whether its representation is implicit or explicit, and an ESD area present in only a few themes might still span several learning domains.

Mother-tongue language education provides a context for such integration. In the textbooks analysed here, sustainability-related issues appeared through reading, listening/viewing, interpretation, discussion, speaking, writing, research, and production. Some were represented mainly in the cognitive and socio-emotional domains, while others also included behavioural opportunities. Sustainability issues can thus become part of the communicative and productive activities of a language lesson without being treated as a separate body of content.

There is still room for broader coverage. Climate Change, Gender Equality, and Sustainable Consumption and Production were relatively underrepresented thematic areas, and behavioural representation was lower than cognitive and socio-emotional representation. These areas could receive further consideration in future textbook development without necessarily increasing the number of sustainability references. What learners are required to do with an issue is also important. Tasks that involve discussion, writing, research, proposing solutions, or planning action can contribute to behavioural engagement if they are meaningfully related to the sustainability issue being addressed.

More specifically, future textbook authors could incorporate reading and writing tasks on climate-related challenges, discussions and text analyses addressing gender equality, and activities examining responsible consumption and resource use. These topics could be linked to purposeful language tasks, such as preparing awareness messages for a defined audience, developing proposals to reduce waste in the school environment, or producing texts that advocate inclusive practices. Such activities would provide opportunities to connect sustainability-related understanding with communicative action, provided that the tasks require students to propose, plan, or undertake a meaningful response rather than merely describe an issue.

The four textbooks show a mixed picture of ESD representation. Sustainability is clearly visible in parts of the corpus and, when identified at the domain level, is usually explicit. However, its distribution is uneven. Looking only for the presence of sustainability content would miss this variation. Thematic coverage, learning-domain representation, and the distinction between implicit and explicit representation each reveal a different aspect of how ESD is incorporated into these Turkish language textbooks.

Limitations and Future Research

The results should be interpreted within the scope of the corpus. Only four Turkish language textbooks were included, covering Grades 5 and 6 at the current stage of TYMM implementation. The results therefore apply to these textbooks and should not be taken as an evaluation of TYMM as a whole or of Turkish language textbooks in general. This limitation may become less restrictive as materials for other grade levels become available. It would then be possible to examine whether the patterns found here continue across grades or change as the curriculum progresses. Subsequent editions of these textbooks could also be compared with the present corpus to track changes in ESD representation over time.

Another constraint comes from the nature of textbook analysis. What was coded in this study was what the materials offered, not what happened in classrooms. A behavioural opportunity in a textbook does not mean that students actually engage in the proposed action or develop the related sustainability competence. Nor does a zero code mean that the topic cannot enter the lesson. Teachers may introduce an issue that is absent from the textbook, extend what is provided, or approach it critically in classroom discussion. Classroom observation would therefore provide a useful direction for follow-up research. Interviews or focus groups with teachers and students, together with student work, could also show how textbook-based ESD opportunities are interpreted and used in practice. At the same time, ESD extends beyond textbook content and classroom instruction, as whole-institution approaches also emphasise the role of learning environments, institutional practices, and community engagement in sustainability education [3].

There are also limitations related to the coding itself. While the operational definitions, criteria, and boundary rules were set in advance of the final analysis, decisions regarding implicit or explicit representation and the three learning domains required interpretation. The level of intercoder agreement also indicates that some distinctions within the framework required interpretive judgement, particularly when differentiating implicit from explicit representation and when assigning evidence across closely related thematic areas or learning domains. The disagreements were then reviewed together using the textbook evidence and the predetermined criteria, and the final codes were agreed upon. Several of these cases occurred at the boundaries between related concepts. For instance, cultural heritage was not assumed to represent Cultural Diversity and Tolerance, weather was not assumed to represent Climate Change, nature was not assumed to represent Environmental Sustainability, female figures were not assumed to represent Gender Equality, conflict was not assumed to represent Peace and Non-violence, and technology was not assumed to represent Sustainable Consumption and Production. Applying the same framework to a different textbook corpus could show whether similar boundary cases recur and whether some of the coding criteria require further clarification.

A further limitation lies in the choice of analytical framework. The study used eight GCED/ESD thematic areas together with UNESCO’s cognitive, socio-emotional, and behavioural learning domains. This provided a common basis for examining all 12 themes, but other frameworks would not necessarily produce the same analytical picture. Looking at the textbooks through individual SDGs or sustainability competencies, for example, might draw attention to content that is less visible within the framework used here. Comparing different frameworks applied to the same material could therefore provide another direction for future research.

Finally, Turkish language is only one part of the curriculum. Limited representation of an ESD area in these textbooks does not tell us how much attention it receives elsewhere. Climate Change, for example, may be addressed differently in science or social studies. A cross-disciplinary analysis of several school subjects could show whether ESD areas that receive little attention in Turkish language textbooks are addressed elsewhere or remain limited across subjects. Comparisons with mother-tongue and foreign-language textbooks from other countries could provide another perspective on which patterns are specific to this corpus and which also appear in other educational contexts.

The present study is thus limited to what can be established from these four textbooks and the analytical framework used to examine them. Questions remain beyond the textbooks themselves: how these opportunities are used in classroom practice, whether their representation changes across later grade levels and textbook editions, and how the patterns identified here compare with those in other subjects and educational contexts.