The Importance of School Principals’ Values towards the Inclusive Education of Disabled Students: Associations between Their Values and Knowledge, Beliefs, Attitudes and Practices

: The current paper presents part of a broader, large-scale study regarding inclusive education and educational leadership in Greece that highlights the decisive role that school principals’ values play into shaping inclusive education. Its proposed theoretical model, based on extensive bibliographical research, explores the relationships between values, and knowledge, beliefs, attitudes and practices regarding the education of disabled students, highlighting that school principals’ values inﬂuence their beliefs and attitudes, and by extension their inclusive practices. Thus, the current paper presents a large-scale research on the proposed theoretical model with a representative sample of Greek primary and secondary education school principals. The data were collected with a composite questionnaire adapted and validated for the Greek context, which was electronically administered to a sample of 582 school principals from 334 primary and 248 secondary schools. The results of a hierarchical multiple regression analysis and a pathway analysis were interpreted based on the strength and direction of the relationships between the examined variables, as well as their signiﬁcance. The hierarchical multiple regression analysis revealed that school principals’ knowledge and beliefs regarding the education of disabled students, and to a lesser extent their values, predicted whether school principals implement practices regarding the education of said students in their school units. However, school principals’ values were indeed the strongest predictive factor for their attitudes towards the education of disabled students and along with their knowledge, play a catalytic role in shaping their beliefs, attitudes and by extension, their practices regarding the education of disabled students. The pathway analysis conﬁrmed the schematic representation of the regression relationships between the examined variables which showed that the theoretical model captures the predictive relationships among the variables, identiﬁes potential causal pathways and showcases their decisive role in inclusive educational leadership. In short, the theoretical model demonstrates a very good ﬁt to the research data coming in agreement with the results from both statistical analyses. Thus, it outlines a consistent and coherent outcome, which highlights multiple relationships between the variables, but primarily the multilayered effect of values in the case of inclusive educational leadership.


Introduction
This paper aims to examine the importance of school principals' values towards the inclusive education of disabled (This paper chooses not to endorse an approach to disabilities and/or SEN from a deficiency point of view.Regarding the controversial dilemma of the terminology "person with a disability" or "disabled person" and the long, heated debate on the 'correct' language to use when talking about disability, we consider that both terms may be supportive of disability rights and social inclusion.This is because it is through language that ideas and assumptions are shaped, and these, in turn, directly affect the ways people are treated and valued.As Titchkosky [1] has indicated, many people use 'people with disabilities', also referred to as people-first language which is thought to stress the person (or 'personhood') before disability but "it organizes a consciousness of disability as a condition of limitation and lack that some people have" [1] (p. 129).However, in more recent years, the preferred term used by the disabled people's movement is 'disabled person' [2,3].This term stresses the view that disability is something done to a person, not something a person individually has [4] (p. 5).For this reason, and adopting the disability movement perspective, we consciously use the term "disabled people" rather than "people with disability" in the manuscript) students and specifically the interrelationships between their knowledge, beliefs, attitudes and practices regarding the education of disabled students in their school units.As defined by Graham [5] (p.24), inclusion is "a process of systemic reform embodying changes and modifications in content, teaching methods, approaches, structures and strategies in education to overcome barriers with a vision serving to provide all students of the relevant age range with an equitable and participatory learning experience and environment that best corresponds to their requirements and preferences" [General Comment 4 adopted by CRPD-UN, 2016 §6] [5] (p.24).Inclusive education stands in need of new thinking and practices, changes in the policies, perceptions, values and principles in terms of schooling, curriculum, pedagogy and assessment [6].This paper focuses on one of the factors commonly associated with the promotion of inclusive education for disabled students in the school units, which is educational leadership [7][8][9][10][11][12] and in particular on school principals and their role as gate keepers in promoting inclusive education [7,9,10,[12][13][14][15][16].
Inclusive education is a call for a total reform of the educational system [17], where school leaders must contemplate on their role in managing their school units from scratch [18].Education is not divided in special and general, as there is no separation between students and is based on the principles of equal access, representation, participation and success for all the students [4,[19][20][21].Hence, it is inextricably linked to inclusive leadership [11,22] which presupposes acceptance, respect, listening, clarifying language and being comfortable with diversity and ambiguity [23,24].
Inclusive educational leadership leads to positive outcomes for the achievement of all students in inclusive schools [11,24,25], "based upon alternative views of the world and the nature and form of schooling that will build that world" [20] (p.25).In fact, school principals committed to creating inclusive schools that meet the academic-social-emotional needs of all students, including disabled students [26], embed through their values, the culture, policies and practices that promote inclusive education at all levels [5,[27][28][29].After all, "education systems are central to the contestation of political and social values, school principals, as citizens, are participants in those struggles" [23] (p.21).Thus, their values establish and influence school culture [7, 27,30], teachers' attitudes and beliefs [31] and therefore, play an important role in implementing and promoting inclusive education [27,30,32].
School principals' values and knowledge are linked to their beliefs about inclusive education, while their values, beliefs and attitudes towards inclusion lead to more inclusive practices [7, 13,29,[31][32][33].Identifying the motivational basis that stems from school principals' personal values can lead to a deeper understanding about why certain school principals hold more positive beliefs and/or attitudes towards the inclusive education of disabled students and can shed light on the relation between school principals' personal values and their knowledge of and practices for inclusive education [7, 16,26,34,35].It is expected that school principals who appreciate diversity and recognize it as an opportunity rather than a barrier embrace the pertinent values along with the appropriate knowledge, beliefs and attitudes regarding the inclusive education of disabled students, hence promote learning opportunities through educational programs and curriculums that convey the needs of all students, including disabled students [7, 16,26,29,34,35].
From the above, the importance of school principals' values jointly with their knowledge, beliefs, attitudes and practices towards the inclusive education of disabled students is Educ.Sci.2023, 13, 360 3 of 21 highlighted as a linchpin for inclusive education in general schools.Albeit school leadership has failed to aptly promote inclusive education adequately [22], there has been little focus on the decisive role of school principals' values in promoting inclusive education for disabled students and in general [28,29,31].This paper highlights the importance of investigating the values of educational leadership in promoting inclusive education, underlining that a school principal's role is both complex and ever-evolving [36,37].
This paper forms part of a broader study regarding inclusive education and school leadership.Specifically, this paper jointly investigates the attitudes, knowledge, beliefs and practices of Greek primary and secondary educational school principals regarding the inclusive education of disabled students in their school units, and whether school principals' values are a predictive factor of the above variables.Generally speaking, the Greek educational system utilizes an integrationist approach to the education of disabled students involving resource room units/pull-out programs, parallel support, sporadic meetings between general educators, special educators and school principals and consultations from special support staff (phycologists, social workers etc.).This paper focuses on a specific subset of questions of the original research that relate to the values of school principals and how these values associate to the rest of the variables under investigation in a proposed theoretical model.
Based on the above, this paper aims to examine: 1. the multiple relationships between values, attitudes, beliefs, knowledge and practices of school principals regarding inclusive education.

2.
the extent to which the investigated variables (values, beliefs, knowledge and practices) predict attitudes.

3.
the extent to which the investigated variables (values, beliefs, attitudes and knowledge) predict practices.

4.
the extent to which the proposed theoretical model fits to the predictive relationships among the investigated variables.

Theoretical Framework
Inclusive education is often disconnected from the wider educational context [6] and falls short of a dense, solid and specific focal point that may often lead to its misconception, misapprehension and by extent to its confused practice.In other words, the goal and objectives of inclusive education are embraced in theory only by national educational policy and do not enhance the essence of the dominant educational approach.This translates into adopting a rhetoric about inclusion without real institutional changes to the wider educational context.Thus, it is not unusual that one can find inclusive institutions and practices alongside remnants of special education, undifferentiated curriculums and teaching methods, as well as the latent expectation for all children to meet the same educational goals.Contrary to the official proclamations of Greece, the ethical appeal of inclusion has been embraced in theory only and while it was coined into national legislation, this has not been implemented in practice.Inclusive education has not been critically approached, but was mistranslated to serve fleeting political agendas and, as a result, falls short of its mission, or rather, it aims to support the mission of general educational policy [6,21,38].However, as Slee [21] (p.913) emphasizes, "inclusive education framework expects that we take up the problem of exclusion as a substantive curriculum concern [ . . .] as an opportunity to model different social relations and possibilities".
Therefore, in addition to the reconstruction of existing educational policies, its implementation requires an in-depth examination of the values and beliefs on which these policies were based on in the first place [7,39].This means that aside school conditions such as the classroom environment or teaching and social problem-solving strategies [40,41], factors such as the attitudes, beliefs and knowledge of the educational staff are also key elements for the successful implementation of inclusive education [27,29,40,42,43].
The promotion of inclusive education requires changing the school culture [44,45] and specifically the educational staff's attitudes, beliefs and mindset [13,24,31,32].Since educational leadership in general [12,46] and school principals in particular [14,47] establish and influence school culture and teacher attitudes, they play an important role in implementing and promoting inclusive education [13,31,[48][49][50][51].Therefore, in order for school principals to move in a more inclusive direction, they have to embrace the success and academic achievement of all students by pursuing high academic expectations for all of them [5,9,[27][28][29][30]51,52].
Given the conceptual ambiguity of these terms (values, beliefs, attitudes and knowledge) it is necessary to first define them briefly, including their interconnections and potential overlaps.Values are diverse, tend to be universal and enduring [13,33], predict how individuals respond to dilemmas/decisions, influence individuals' behavior, choices, emotions and will [53], and they are linked to motivation and thus direct, justify or explain attitudes, norms, behaviors and actions as guiding principles [54].Beliefs are the information that individuals form about a specific event, object or person through their personal values, and crystallize through their knowledge and experiences [29,33,55].Individuals' knowledge influences their beliefs and consequently their attitudes [56].Attitudes are linked to readiness for action as they contain cognitive, affective and behavioral components [13,57].Attitudes translate into choices and form the way individuals express or apply their beliefs and values, and they are influenced by their subject-matter knowledge [13,55,58].Conversely, attitudes influence the transfer of knowledge and skills into practice (potential behavioral manifestation) [13,16,59].Thus, the values, knowledge, beliefs and attitudes develop interdependently in all individuals.
Therefore, the task of school principals who aim at an inclusive leadership is a multifaceted and complicated undertaking.More specifically, they should focus on creating an inclusive culture of equity and establishing access to quality education for all their students in their school unit [31,32,35,50,51].They should account for differentiation, curriculum redesign and enrichment by modifying teaching practices and differentiating teacher roles through the designing and promotion of new enhanced educational practices and by influencing the way in which teachers shape their educational practices in order to respond more effectively to all the students' different needs [12,46,48,52,53].Furthermore, school principals can establish appropriate inclusive conditions by promoting teachers' training on inclusive education and by having the appropriate knowledge regarding differentiated instruction and resolving parents' questions on inclusive education teaching practices [25,29].School principals can also ensure inclusive conditions by managing and coordinating curriculum and instructional resources in ways that support inclusive education [15,32], monitoring, supporting and continuously encouraging all students' personal progress [51].
A first milestone to making schools more inclusive is for school principals to adopt values of inclusive education, such as integrity, self-awareness, transparency, ethical behavior, democracy, equality, respect, cooperation, acceptance, just and equitable educational opportunities for the success of all students, defense of and respect for diversity as an enriching element, creating a classroom community that values diversity and uses all students' experiences and creating accessible and supportive learning environments for all [13,25,60].Moreover, through their leadership, school principals should define and clearly articulate a vision that incorporates the values of inclusive education, with the aim of changing the habits and practices of their school unit [25,52,61], as in this way, they can inspire and guide their teachers to revise their values and adopt more inclusive ones while reinforcing new understandings of diversity [12,15,25,61].School principals are the main actors and transmitters of their values in their schools through their behavior and those who intentionally and responsibly construct a clear value system tend to use all their influence to faithfully implement it in their schools [62].A school principal's values are reflected in their behavior and words [13,28,53], in that their leadership directs the educational matters and the procedures concerning their school's operation [54].Therefore, efforts to develop inclusive schools should be based on inclusive values embraced by the entire school community [5] where school principals act as beacons [5,[27][28][29].To sum up, school principals' leadership is pivotal for inclusive education [27,32,48] and school principals' values [6,7,28], their knowledge and beliefs [29,30,51,63,64] and their attitudes towards disability and inclusive education in general [13,16,31,65] are significant factors that influence their leadership in promoting inclusive education.
Research findings highlight the relationship between school principals' beliefs and attitudes for promoting inclusive practices; this relationship is not only convergent, but may also be divergent [16,35,66].School principals' beliefs are linked to elements of their identity, such as their personal values that also influence their attitudes [13,28,54,67] and by extension their educational practices which shape a school's culture [7,25,32].
Committed school principals who introduce and embed the culture, policies and practices to achieve inclusive education at all levels value diversity, are non-conformist and have the power to lead others by example [5], "based upon alternative views of the world and the nature and form of schooling that will build that world" [20] (p.25).They are also characterized as people who share leadership responsibilities [52], take risks, invest in the development of interpersonal relationships, are actively involved in educational processes, do reflection, have insight and goal setting [9,11].Therefore, to effectively change school culture towards a more inclusive direction, it is essential to review the values on which this change is based, which are influenced and shaped by school principals' personal values [7,68].
School principals' knowledge of educational processes is linked to their beliefs about inclusive education [29,63,64].Strengthening the knowledge of school principals in educational matters in general and in the education of disabled people in particular, is an important need that has been underlined in relevant research [16,29,50].However, many school principals receive little or no formal in-service training regarding knowledge on inclusive education and/or on disability issues [29,34,50,64].
School principals' knowledge of inclusive education affects their provided guideline principles [50].School principals who state that they have more knowledge in education in general and in education of disabled students in particular, have more positive beliefs about inclusive education and are involved in more aspects of its programs [29,63,64].Furthermore, knowledge in education in general [58] and in the education of disabled students in particular [29,58,63], and school principals' beliefs about inclusive education, affect the education of all students in the school unit [64].
Given that individuals' attitudes imply that they act in a certain way towards a goal, it is very important to ascertain whether school principals support or oppose the inclusive education of disabled students.If school principals act according to their stated attitudes, then those who oppose them hinder inclusive education for disabled students, their parents or even for teachers who support inclusive education [13].The successful implementation of new inclusive educational practices is linked to school principals' positive attitudes towards inclusive education [8, 13,14,31,35,52,65].School principals' attitudes influence the attitudes of teachers and other members of the school community and create favorable conditions that allow the acceptance and effective education of all students, including disabled students [13,14,31,49,69].
Individuals' attitudes, which constitute readiness for action [57], are influenced and motivated by their values and beliefs [67].Therefore, changing educational practices does not only require new skills or knowledge from the school principals, but also their positive attitudes, beliefs and values towards inclusive education [16,64].This translates into an imperative need for radical change, educational reform and social justice [5,6,21].
The important role of school principals' values in educational leadership has been scarcely studied both in Greece [28,68] and internationally [70], and such studies are mainly of a qualitative or theoretical nature [68,71,72].To the best of our knowledge, there is no prior research on the correlations between school principals' values and their attitudes, beliefs, knowledge and practices regarding the inclusive education of disabled students to underline the significance of school principals' values and more generally the values of inclusive educational leadership in the education of disabled students.These factors (values, knowledge, beliefs, practices, attitudes) are this study's research variables that are examined with quantitative research instruments.The following theoretical model (Figure 1) emerges through the thorough literature review and the broader study's statistical analyses; subsequently, a hierarchical multiple regression analysis (HMRA) and a pathway analysis have reinforced this theoretical model.
The important role of school principals' values in educational leadership has been scarcely studied both in Greece [28,68] and internationally [70], and such studies are mainly of a qualitative or theoretical nature [68,71,72].To the best of our knowledge, there is no prior research on the correlations between school principals' values and their attitudes, beliefs, knowledge and practices regarding the inclusive education of disabled students to underline the significance of school principals' values and more generally the values of inclusive educational leadership in the education of disabled students.
These factors (values, knowledge, beliefs, practices, attitudes) are this study's research variables that are examined with quantitative research instruments.The following theoretical model (Figure 1) emerges through the thorough literature review and the broader study's statistical analyses; subsequently, a hierarchical multiple regression analysis (HMRA) and a pathway analysis have reinforced this theoretical model.

Participants
The sample was extracted with a two-stage stratified sampling from the updated records of primary and secondary schools with "resource room units ("Resource room units" are pull-out programs operating in mainstream education where children identified as having special education needs and/or disabled students participate and receive support on an individualized basis for some hours during the school week.The existence of resource room units was one of the selection criteria for schools to participate in the current study to ensure that the participating schools accommodate disabled students as well"), as provided by the Department of Special Education of the Greek Ministry of Education.The questionnaire was fully answered by 581 school principals (Table 1), exceeding the required size for its representativeness.From the outset, it was made clear to the participants that their anonymity was guaranteed and that this study's research results would be exclusively used for academic and research purposes

Participants
The sample was extracted with a two-stage stratified sampling from the updated records of primary and secondary schools with "resource room units ("Resource room units" are pull-out programs operating in mainstream education where children identified as having special education needs and/or disabled students participate and receive support on an individualized basis for some hours during the school week.The existence of resource room units was one of the selection criteria for schools to participate in the current study to ensure that the participating schools accommodate disabled students as well"), as provided by the Department of Special Education of the Greek Ministry of Education.The questionnaire was fully answered by 581 school principals (Table 1), exceeding the required size for its representativeness.From the outset, it was made clear to the participants that their anonymity was guaranteed and that this study's research results would be exclusively used for academic and research purposes This study's socio-demographic results (Table 1), highlight an "aging population" of school principals in Greece as the majority of the sample is over 55 years old.This finding confirms the results of other similar research, as for many years and up to recently, seniority was the main criterion for a managerial position instead of academic qualification [73].Furthermore, the managerial position in the school units is male dominated, with men in the sample predominant over women, although women tend to participate more in completing research questionnaires than men [74].Consequently, male teachers occupy managerial positions more than female teachers even though the number of female teachers in Greece is significantly greater than that of men [75].
The majority of Greek school principals have a long experience in education with more than 20 years of teaching experience in general education.However, they have almost zero teaching experience in special education.They tend to remain in this position for many years, with over a quarter of the sample serving as school principals for 20 years or more.More than half of them hold a master's degree, but few hold a doctorate.However, due to the criterion of seniority, more than a quarter of them remain in a managerial position with only the basic degree [73].Most school principals state that they have not received any training regarding the education of disabled students, while those who have received state that it was not sufficient.More generally, most of them state that the level of their training as school principals is not satisfactory, let alone their training regarding the education of disabled students.These findings highlight the need for substantial and continuous training of school principals, especially regarding the education of disabled students [76,77].Indeed, school principals consider their training necessary, especially in matters concerning the education of disabled students [76], as the possession of scientific knowledge on modern learning theories and teaching methods enhance school principals' ability to effectively cope with and meet the learning needs of all their students [73].
Three quarters of the school principals are not quite satisfied with the adequacy of the logistical infrastructure of their school unit regarding the education of disabled students.Moreover, most school principals do not have personal experience with a disabled person other than a student in their school unit.This, however, is a characteristic of Greek society [78], as people with disabilities are socially excluded and are led to social isolation.Although it is reprehensible that individuals belonging to the field of education show such a high rate of non-contact with a disabled person, the Greek education system itself reflects the dominant social and moral values of Greek society, which orients itself towards "homogeneity and the concept of the average" [78] (pp.80-81).

Research Instrument
For the purpose of this study, three survey instruments have been selected to measure the corresponding variables: (a) portrait values questionnaire (PVQ) [33] is used for the study of the values of school principals of primary and secondary education in Greece; (b) principals' knowledge of fundamental and current issues in special education (PKISE), developed by Wakeman et al. [64] is used for the study of school principals' knowledge, beliefs and practices; (c) principals' attitudes toward inclusive education (PATIE) scale, developed by Bailey [13], is used for the study of attitudes towards inclusive education.All the above-mentioned instruments (PKISE/PVQ/PATIE) are adapted and validated for the Greek context.Along with a section collecting the school principals' socio-demographic information, they form this study's research instrument.
Analytically, the first section of the unified questionnaire examines school principals' socio-demographic and professional characteristics and consisted of nineteen (19) statements.The second section examines school principals' beliefs, with six (6) statements, and practices, with seven (7) statements towards the education of disabled students.The response scale for both beliefs and practices is a three-point Likert scale: 'Agree', 'Disagree' and 'I have no opinion'.
The third section examines school principals' level of knowledge regarding the education of disabled students with twenty-two (22) statements in a four-point Likert scale: 'Don't know', 'Limited knowledge', 'Basic knowledge', 'Complete knowledge'.The fourth section examines school principals' attitudes towards the education of disabled students with twenty-nine (29) statements on a five-point Likert scale: 'Strongly Disagree (DA)', 'Disagree (D)', 'Neutral (O)', 'Agree (S)', 'Strongly Agree (SA)'.The last and fifth section examines school principals' values according to the ten self-referential values (security, tradition, conformity, benevolence, universalism, self-direction, stimulation, hedonism, achievement, power) of Schwartz's theoretical model [33] and the organization of these into four 'higher order values-HOV' (Conservation: Security, Tradition, Conformity; Openness to change: Self-Direction, Stimulation, Hedonism; Self-enhancement: Power, Achievement; Self-transcendence: Benevolence, Universalism) [67], with forty (40) statements which are presented as short verbal portraits of the goals, desires and aspirations of different individuals, on a six-point Likert scale: 'Not like me at all', 'Not like me', 'A bit like me', 'Somewhat like me', 'Like me', 'Very like me'.

Validation
From the exploratory factor analysis of "PKISE", two factors emerged for the variable of knowledge: (a) 'Fundamental knowledge regarding the education of students with D/SEN' Cronbach's a = 0.930 and (b) 'Knowledge of current issues regarding the education of students with D/SEN' Cronbach's a = 0.861.The overall scale of knowledge has Cronbach's a = 0.940.For the variable of beliefs only one factor emerged with Cronbach's a = 0.561.Likewise, the variable of practices is unifactorial with Cronbach's a = 0.685.
From the exploratory factor analysis of "PATIE", three factors emerged for the variable of attitudes: (a) 'Placement of students with D/SEN in general classes' with Cronbach's a = 0.850, (b) 'Co-education of students with and without D/SEN in general classes' with Cronbach's a = 0.805 and (c) 'School unit's adequacy regarding the education of students with D/SEN' with Cronbach's a = 0.693.The overall scale of attitudes has Cronbach's a = 0.851.

Procedure
The questionnaire was administered electronically to the school principals via Google Forms and was validated for a total sample of 581 school principals from 334 primary and 248 secondary Greek schools."PATIE" and "PVQ" have been previously adapted for the Greek context by Platsidou and Tsiolpidou [69] and Pavlopoulos [79], respectively.However, Platsidou and Tsiolpidou modified some statements of Bailey's [13] original questionnaire, and thus, an exploratory factor analysis was carried out to validate "PATIE", as the present study is based on the original instrument as formulated by its manufacturer Bailey [13].A confirmatory factor analysis was conducted for "PVQ" and an exploratory factor analysis was conducted for "PKISE".The validated questionnaire featured high reliability scores: "PATIE" has Cronbach a = 0.839; "PVQ" has Cronbach a = 0.844 for the 10 values and Cronbach a = 0.831 for the 4 higher-order values-HOV; "PKISE" accordingly has Cronbach a = 0.943.

Data Analysis
HMRA is used to determine the amount of variance in the dependent variable that is explained by the independent variables when entered in a particular order.The more variance an independent variable accounts for, the more important that variable is likely to be.By performing a HMRA, it was investigated to what extent school principals' values are predictive factors for their attitudes and practices regarding the education of disabled students.
Structural equation modeling (SEM) is widely used in the social sciences to simultaneously estimate multiple equations with mutual effects and to test complex causal theories with multiple pathways, incorporating variables with multiple indicators [80].As a subcategory of structural equation models, pathway analysis is a confirmatory methodological approach that allows the use of correlational data to investigate a range of predictive relationships.In this study, pathway analysis is used to find the relationship between the values of Greek primary and secondary Education school principals and their knowledge, beliefs, attitudes and practices regarding the education of disabled students, as portrayed in the theoretical model (Figure 1).

Results
The following table (Table 2) presents the results of the HMRA with the practices of school principals regarding the education of disabled students as dependent variable and the following in place of the independent variables: the two factors of their knowledge regarding the education of disabled students, their beliefs regarding the education of disabled students and the ten factors of their values.Table 2 shows that school principals' fundamental knowledge and their knowledge of current issues regarding the education of disabled students predict their practices regarding the education of disabled students as they account for the largest percentage of the variance of the dependent variable of practices, which is 10%.The values of school principals appear to predict, but to a lesser extent, their practices regarding the education of disabled students as they account for 7% of the variance of practices.The beliefs and attitudes of school principals hardly predict their practices regarding the education of disabled students, as they account for only 2% and 1% of its variance, respectively.As a whole, school principals' knowledge, beliefs and attitudes regarding the education of disabled students, as well as their values, predict whether they implement educational practices regarding the education of disabled students, as all the independent variables combined account for 20% of the variance in the dependent variable.
The following table (Table 3) presents the results of the HMRA with the first factor of the school principals' attitudes regarding the education of disabled students as dependent variable and the following in the place of the independent variables: the two factors of their knowledge regarding the education of disabled students, their beliefs regarding the education of disabled students and the ten factors of their values.Table 3 shows that school principals' values predict the first factor of their attitudes regarding the placement of students in general education classes of their school unit, as they account for the largest percentage of the variance of the dependent variable, which is 15%.The school principals' beliefs regarding the education of disabled students appear to predict, but to a lesser extent, the first factor of their attitudes, as they account for 11% of its variance.Their fundamental knowledge and their knowledge of current issues regarding the education of disabled students appear to predict, at a lower percentage, their attitudes regarding the placement of disabled students in general education classes of their school unit, as they together account for 7% of its variance.
The following table (Table 4) presents the results of the HMRA with the second factor of the school principals' attitudes regarding the education of disabled students as the dependent variable and the following in place of the independent variables: the two factors of their knowledge regarding the education of disabled students, their beliefs regarding the education of disabled students and the ten factors of their values.Table 4 shows that school principals' values predict the second factor of their attitudes regarding the co-education of disabled students and students without any current disabilities in general education classes of their school unit, as they account for the largest percentage of the variance of the dependent variable of the second factor of attitudes, which is 22%.School principals' fundamental knowledge and their knowledge of current issues regarding the education of disabled students appear to predict, but to a lesser extent, the second factor of their attitudes, as they are responsible for 10% of its variance.School principals' beliefs regarding the education of disabled students predict less the second factor of their attitudes, as they account for only 8% of its variance.
The following table (Table 5) presents the results of the HMRA with dependent variable the third factor of the school principals' attitudes regarding the education of disabled students and the following in place of the independent variables: the two factors of their knowledge regarding the education of disabled students, their beliefs regarding the education of disabled students and the ten factors of their values.Table 5 shows that school principals' values predict the third factor of their attitudes regarding the adequacy of their school unit for the education of disabled students, as they are responsible for the greater percentage of the variance of the dependent variable of the third factor of attitudes, which is 8%.Similarly, school principals' fundamental knowledge and knowledge of current issues regarding the education of disabled students significantly predict the third factor of attitudes, accounting for nearly as much, i.e., 8% of its variance.School principals' beliefs regarding the education of disabled students predict little if at all the third factor of their attitudes, as they account for only 0.05% of its variance.
From the above, school principals' values are the strongest predictor overall for their attitudes towards the education of disabled students.They predict their attitudes, accounting for the largest proportion of the variance of the first factor at 15%, the second factor at 22% and the third factor at 8%.However, they do not strongly predict their practices regarding the education of disabled students, as they account for 7% of the variance in the dependent variable of practices.Instead, school principals' fundamental knowledge and their knowledge of current issues regarding the education of disabled students predict their practices regarding the education of disabled students, as they account for the largest percentage of its variance, at 10%.They are also found to predict, to a lesser extent than school principals' values, their attitudes, accounting for 7% of the variance of the first factor, 10% of the second factor and almost 8% of the third factor.

Results of Pathway Analysis
In a pathway analysis model, variables that are on the left side and do not have an arrow tip pointing at them are considered exogenous variables, and their variance is caused entirely by variables not included in the model.In the theoretical model under consideration (Figure 2), the factors of school principals' knowledge (two factors) and their values (ten factors) are considered exogenous variables.Bidirectional lines connecting knowledge with values show the correlation between these variables and is not a causeand-effect relationship.

Results of Pathway Analysis
In a pathway analysis model, variables that are on the left side and do not have an arrow tip pointing at them are considered exogenous variables, and their variance is caused entirely by variables not included in the model.In the theoretical model under consideration (Figure 2), the factors of school principals' knowledge (two factors) and their values (ten factors) are considered exogenous variables.Bidirectional lines connecting knowledge with values show the correlation between these variables and is not a cause-and-effect relationship.In contrast, variables that have arrow tips pointed at them are called endogenous, In contrast, variables that have arrow tips pointed at them are called endogenous, that is, they are dependent variables insofar as their variation is explained by one or more variables within the model as well as any other exogenous factors.The factors of attitudes (three factors), beliefs (unifactorial) and practices (unifactorial) of school principals are considered endogenous variables, with those of beliefs and attitudes being mediators.Mediating variables lie between the dependent and the independent variable, since instead of assuming only the direct effect of the independent variable on the dependent, it is assumed that the independent variable may also affect first the mediating variable and then the dependent variable (indirect effect).
The numbers on the arrows (Figure 2) connecting two variables express how one variable is related to the other.The higher the number, the stronger the relationship between the two variables.The sign describes the direction of the relationship where the positive sign implies that as one variable increases, the other increases as well.The negative sign implies that as one variable decreases, the other increases.The circles symbolize any errors included in these measurements, while the weighted "standardized loadings" values are used in the diagram, as they allow the comparison of the loadings of the factors, facilitating the interpretation of the data.
Various criteria are used to interpret the results and to determine whether the theoretical model has practical validity, since the correct interpretation of the data from a model does not depend on one indicator alone, but on many together.Specifically, the value of the x 2 chi-square index shows the overall fit of the hypothetical model to the empirical data and must give a statistically non-significant result (p > 0.05), while the smaller the value, the better for the data interpretation model.Because the x 2 statistical significance test depends on sample size and usually rejects the model for samples larger than 200, it is recommended to use the normed chi-square: (x 2 /Degrees of freedom) index which should show values less than 4 or 5, with ideal values below 3 or 2 [81].Due to the large sample size, this study's model has a weighted index x 2 /df = 1.66, which corresponds to the ideal values of this index of fit of the model to the data.
In addition, to evaluate the fit of the model, the CFI (comparative fit index) and TLI (Tucker-Lewis index) indices are checked, which take values between 0 and 1, while values above 0.95 are ideally accepted.In addition, the RMSEA (root mean square error of approximation) and SRMR (standardized root mean square residual) indices are checked, which are considered acceptable when they present values less than 0.08 or 0.05, respectively [81], using the 90% confidence interval CI = 90%.In this study's model, the RMSEA index = 0.03 is an ideal value for fitting the model to the data.Also, some incremental fit indices are checked: CFI, GFI, NNFI, TLI, RFI and AGFI which must have a value greater than 0.90 for a good fit of the model.In this study's model, the above indexes take the following values: CFI = 1.00,GFI = 1.00,AGFI = 0.95, which indicate the good fit of the model to the data (Table 6).Thus, due to the goodness of fit indices of this study's theoretical model, no modifying indices had to be used.In summary, as can be seen from the theoretical model under consideration (Figure 1), the route diagram of the present research shows a total of five variables, of which knowledge and values are the exogenous variables while all the others are endogenous variables.Out of these, practices are the dependent variable, while beliefs and attitudes are mediators.Relationships depicted by the pathway analysis are statistically significant at p < 0.001 and p < 0.05.
As can be seen in Figure 1, the effect of school principals' knowledge regarding the education of disabled students is positive on both their attitudes and their practices.The effect of school principals' values is positive both on their beliefs and attitudes and on their practices regarding the education of disabled students.Finally, school principals' beliefs have a positive effect on both their attitudes and their practices regarding the education of disabled students, and finally, their attitudes, while not being the only or most decisive factor, have a positive effect on their practices regarding the education of disabled students.
In conclusion, according to the indicators assessed, the goodness-of-fit indices of this study's theoretical model to the data are very satisfactory.Specifically, x 2 (4, n = 581) = 6.65, x 2 /df = 6.65/4 = 1.66,CFI = 1.00,GFI = 1.00,AGFI = 0.95, RMSEA = 0.03, CI = 90%, which corroborate this study's literature documentation as well as the results of its previous statistical analyses, such as the HMRA, which contributed to the strengthening of this study's theoretical model.

Discussion
This paper aims to examine the importance of school principals' values for the inclusive education of disabled students as well as the interrelationships of these values to their knowledge, beliefs, attitudes and practices regarding the education of disabled students in their school units.
The results of the HMRA highlight school principals' values as the strongest predictive factor for their attitudes (placement, co-education, efficacy) regarding the education of disabled students in general classes of their school units.This is the key insight, as values affect the formation of a set of principles and standards, which determine the appropriate and acceptable way of behavior [16,39] and thus constitute the strongest predictive factor for the attitudes that translate into a possible manifestation of behavior [13,16].Therefore, school principals' values are important factors that affect not only educational reforms, but all their actions regarding the education of disabled students [7].From a broader perspective, they influence their role as school leaders in promoting the education of disabled students [9,10,[26][27][28]68].
Moreover, the results point out that school principals' knowledge regarding the education of disabled students is the strongest predictor for the promotion and implementation of their practices regarding the education of disabled students, in agreement with Pregot [29] and Pazey et al. [34], who argue through knowledge, school principals feel more prepared and qualified to effectively implement appropriate practices for the education of these students.Furthermore, Segall and Campbell [82] support that school principals' knowledge combined with experience leads to appropriate awareness, and through this, to the promotion and implementation of effective educational practices that respond to the needs of all students in the school unit.However, as mentioned, Greek school principals have neither significant experience [83] nor significant-let alone joint and coordinated-training regarding the education of disabled students [34].
Furthermore, school principals' beliefs are found to fairly predict their attitudes regarding the placement and co-education of disabled students in general education classrooms of their school units, as well as their practices regarding said students, and barely predict, if at all, their attitudes regarding the school's adequacy for the education of disabled students.However, relevant prior research supports that school principals' positive beliefs regarding the education of disabled students effectively contribute to manifesting positive attitudes and implementing practices for their education [16].Also, Graham and Spandagou [84] found in their study that school principals' attitudes are significantly influenced by their beliefs regarding the education of disabled students as well as their overall perception of inclusion.In this study, beliefs do not seem to strongly predict school principals' attitudes and practices could be explained due to the limited number and relatively low Cronbach of the questionnaire statements related to the examination of school principals' beliefs.It could be also attributed, however, to the conceptual disambiguation from knowledge which is examined through separate questionnaire items.Therefore, further investigation of the relationship between school principals' beliefs and their attitudes and practices regarding the education of disabled students is necessary.
One of the most important research results of the present study is the reinforcement of its proposed theoretical model (Figure 1).Notably, the effect of school principals' values is positive both on principals' beliefs and attitudes, and on their practices regarding the education of disabled students.This finding has been pointed out in the literature review since individuals' values and beliefs influence and motivate their attitudes and their behavior [67].It is also concurrent with the HMRA results that show values to be the strongest predictor of school principals' attitudes regarding the education of disabled students.
Moreover, as proposed in the theoretical model, the effect of the school principals' knowledge is positive both on their attitudes and on their practices regarding the education of disabled students, which is in line with the literature review that highlights that an individual's knowledge affects their attitudes [13,55,58,64].This key insight is also supported by the results of the HMRA, where knowledge is found to be the strongest predictor for school principals' practices regarding the education of disabled students.This significant direct effect of school principals' knowledge on their practices regarding the education of disabled students has not been underlined before in the relevant bibliography and is depicted in the revised theoretical model (Figure 3).Furthermore, school principals' beliefs have a positive effect on both their attitudes and their practices regarding the education of disabled students, and finally, their attitudes, while not being the only or most decisive factor, have a positive effect on their practices regarding the education of disabled students.These results are corroborated by the literature review where a statistically strong correlation between school principals' beliefs and attitudes is highlighted in relation to the promotion of inclusive practices [16,35].This insight emerges also from the HMRA results that show beliefs and attitudes to be predictors for school principals' practices, albeit not the strongest.As portrayed the theoretical model (Figure 3), school principals' knowledge is the strongest predictive factor for their practices regarding the education of disabled students.
In conclusion, this study's theoretical model (Figure 3), as derived from a thorough literature review, portrayed a very good adaptation to the rich research data.Simultaneously, the results of both the hierarchical multiple regression and the pathway analysis outline a consistent and coherent picture that comes in agreement with the theoretical model, underlining multiple relationships between the variables and primarily the significant role school principals' values play in the case of inclusive education.
The importance of studying school principals' personal values lies in the fact that school principals manage their schools according to their values and rely on them to decide what is considered right and wrong, acceptable or not [85].Inclusive education is not a practice of special education for disabled students, but an educational process that concerns all students who are different from others and aims not only to place these students in general education classes as part of their inclusion, but to restructure the general school to respond effectively to the heterogeneity of its student population [5,21,39].
Thus, school principals as one of the main factors associated with the promotion of inclusive education of disabled students [7,13,16] establish and influence school culture [7] as well as teacher attitudes and beliefs [13,31,49], and therefore, play an important role in implementing and promoting inclusive education for disabled students [32,48].In addition, the wider school community follows school principals' mandate to achieve consensus [70].Therefore, school principals' personal values end up reflecting in all aspects Furthermore, school principals' beliefs have a positive effect on both their attitudes and their practices regarding the education of disabled students, and finally, their attitudes, while not being the only or most decisive factor, have a positive effect on their practices regarding the education of disabled students.These results are corroborated by the literature review where a statistically strong correlation between school principals' beliefs and attitudes is highlighted in relation to the promotion of inclusive practices [16,35].This insight emerges also from the HMRA results that show beliefs and attitudes to be predictors for school principals' practices, albeit not the strongest.As portrayed the theoretical model (Figure 3), school principals' knowledge is the strongest predictive factor for their practices regarding the education of disabled students.
In conclusion, this study's theoretical model (Figure 3), as derived from a thorough literature review, portrayed a very good adaptation to the rich research data.Simultaneously, the results of both the hierarchical multiple regression and the pathway analysis outline a consistent and coherent picture that comes in agreement with the theoretical model, underlining multiple relationships between the variables and primarily the significant role school principals' values play in the case of inclusive education.
The importance of studying school principals' personal values lies in the fact that school principals manage their schools according to their values and rely on them to decide what is considered right and wrong, acceptable or not [85].Inclusive education is not a practice of special education for disabled students, but an educational process that concerns all students who are different from others and aims not only to place these students in general education classes as part of their inclusion, but to restructure the general school to respond effectively to the heterogeneity of its student population [5,21,39].Thus, school principals as one of the main factors associated with the promotion of inclusive education of disabled students [7, 13,16] establish and influence school culture [7] as well as teacher attitudes and beliefs [13,31,49], and therefore, play an important role in implementing and promoting inclusive education for disabled students [32,48].In addition, the wider school community follows school principals' mandate to achieve consensus [70].Therefore, school principals' personal values end up reflecting in all aspects of their school community and become decisive in terms of the inclusive education for all of its students.
In short, values play a catalytic role in shaping the beliefs and attitudes, and by extension, the practices of school principals regarding the education of disabled students.However, the relationship between values, beliefs, knowledge, attitudes and practices admittedly needs further investigation.Simultaneously, it is equally important to study not only the values of the participants in the disability discourse, but also those behind the policies and ideologies, structure and culture of the society in which this discourse takes place, to effectively promote an open and fruitful public dialogue on inclusive education and to minimize the possibility that "politically correct values are deployed to argue for a position or to silence dissent" [86] (p.19).

Limitations & Future Research
Due to this study's original aim and design, specific limitations must be considered when interpreting its results and potentially serving as scaffolding for future research.This study is based on a large and homogeneous sample in Greece; hence, the results cannot be generalized to other cultural contexts in different national settings.Further studies are required to survey school principals' values jointly with their knowledge, beliefs, attitudes and practices regarding the education of disabled students in other countries, to cross-validate and further refine this study's theoretical model as well as its original research instrument.
Given the findings regarding the values of school principals in relation to their knowledge, beliefs, attitudes and practices regarding the education of disabled students, it is found that school principals' practices can only be interpreted to a small degree by the aforementioned variables.Therefore, an important research area is highlighted for other potential variables that may influence the practices of school principals regarding the education of disabled students, and which do not fall within the scope of this study.Finally, a possible refined research proposal would focus on the thorough investigation of the factors that influence school principals' values for the development of highly motivated inclusive school principals, and whether and to what extent school principals' values differentiate their instructional practices regarding the education of disabled students.

Conclusions
Understanding the influence of school principals' values in relation to the education of disabled students can provide useful feedback to public authorities and other organizations in favor of inclusive education, in their quest to develop effective inclusive policies and programs to support school principal's needs and enhance the appropriate values that surround inclusive leadership.This understanding could also enable educational and training providers at any level to develop effective training consistent with school principals' values for achieving a leadership for inclusion.Such an outlook would be invaluable as the members of educational staff "receive education and training giving them the core values and competencies to accommodate inclusive learning environments" [5] (p.76).
However, it must be noted that the values perspective that promotes social justice and equal participation in education and society cannot provide a justification for the education of disabled students which is usually located on the perimeter of education."It is questionable that the inclusive education movement has really redefined what is viewed to be 'normal' but it has been successful in challenging the boundaries" [23] (p.28).As this study argues, the inclusive education movement can rely upon the understanding of the importance of the values of educational leadership, to lead itself to more solid foundations so it can redefine itself from scratch.
In view of the above, inclusion as an open-ended, value-driven horizon is not subject to an objective evaluation and can never be fully attained.Any effort in this direction is always insufficient and temporary and calls for more effort and resources but brings very real and tangible results in the wellbeing of younger generations.Thus, it needs to be unchained from all material, political, financial or technical limitations and presupposes the sincere cooperation of all stakeholders in the educational process, so that it can amount to anything more than an utopian conception of education and more generally of society.
Therefore, this study's theoretical model (Figure 3) aspires, on one hand, to begin untangling the factors that influence inclusive education and, in particular, to highlight the catalytic role of the values carried by the individuals who move the threads of inclusive education, mainly through their leadership.On the other, it attempts to prove that the road to the redefinition of inclusive education goes necessarily through values, as this reshaping must start from the fundamental elements that define it, which are none other than the values that imbue every individual who deals with its calling.After all, inclusion, much like education itself, is fundamentally a matter of values.

22 Figure 3 .
Figure 3. Revised theoretical model of the predictive relationships between school principals' values and their knowledge, beliefs, attitudes and practices.

Figure 3 .
Figure 3. Revised theoretical model of the predictive relationships between school principals' values and their knowledge, beliefs, attitudes and practices.

Table 2 .
HMRA results on which variables predict practices.

Table 3 .
HMRA results on which variables predict attitudes regarding the placement.

Table 4 .
HMRA results on which variables predict attitudes regarding the co-education.

Table 5 .
HMRA results on which variables predict attitudes regarding the adequacy of their school unit.

Table 6 .
Indices of fit of the theoretical model to the research data.