Equal Opportunities in an Inclusive and Sustainable Education System: An Explanatory Model

: Equal opportunities is an objective to be achieved in a sustainable society, as formulated by various sustainable development objectives. Inclusive education refers to the right of all people to education, guaranteeing the presence, participation, and progress of all students and, above all, equal opportunities. However, today, it is a dual and controversial issue, as it appears among the strategies and objectives planned at international and European levels, but its application and real development is still far from being a right with guarantees. Moreover, the concept of integration remains in most areas and many education policies. Therefore, the objective of this work is to establish which integration and inclusion measures favor equal opportunities. The study offers, as a major novelty, the results of empirical research, which provides a scientific framework to this process of equal opportunities. It is approached from the perspective of teaching staff with a sample of 133 professionals. The results are analyzed through factorial analysis and multiple linear regression. The results show that the aspects related to inclusion (measures of attention to diversity, high knowledge about inclusion, and adapting the system to inclusion) have a significant positive effect. The integration of students reduces equal opportunities in a statistically significant way. The results are of interest for educational policies and for decision-making and strategies to achieve sustainability and inclusion in the school environment.


Introduction
When analyzing the aspects that the international community gathers regarding the right to education, we can verify that they not only contemplate or are limited to the formal aspects referred to educational centers, teachers and students, but they also offer content and regulations concerning equal opportunities [1]. These are reflected in documents of international community (United Nations Human Rights and United Nations Educational, Scientific and Cultural Organization), such as the International Convention on the Rights of the Child [2], the International Convention on the Rights of Persons with Disabilities [3] and its subsequent 2016 report, and even in Sustainable Development Goal 4 (SDG 4), which supports the guiding principles of the World Education Agenda 2030.
When we talk about equal opportunities in education, it does not mean that everyone should learn the same thing, at the same time and in the same way. It means that everyone has the same opportunities to learn without ranking the students. Thus, when we speak of equal opportunities, we refer to the confluence of and respect for differences [4]. It is therefore necessary for the education system to offer equal opportunities to all children, no matter what the differences between them are.
For inclusive education, equal opportunities are a major challenge [5]. At the heart of the idea of inclusive education lie serious issues concerning human rights and equal opportunities [6]. UNESCO [7] states that inclusion is a movement to transform education systems to respond to the diversity of students to realize the right to education with equal opportunities. The implementation of educational inclusion involves working on issues such as social justice and equal opportunities; aspects that are not covered by integration [8].
It is on this premise that we will focus the central proposal of our work: to justify that the model of integration is still insufficient to guarantee equal opportunities and, therefore, does not favor or promote inclusion. This is reaffirmed in the definition of educational integration, which is characterized by a number of fundamental issues. On the one hand, research links it to the medical model of disability [9], which assumes that in disability, the difficulty is in the person and not in the environment, which does not generate the environmental or methodological conditions to guarantee the right to education with equal opportunities. On the other hand, the model of integration proposes that children in isolated facilities are transferred to regular school buildings, but are put in special classes [10], only attending regular classes at variable periods of the school day. In short, the idea is to rehabilitate students with special needs by placing them in environments according to their capacity. This is reflected in its basic approaches, its theoretical foundations, philosophy, or law, centered on justice and equality, which are also echoed in the principles [11] and objectives of educational inclusion [12][13][14][15].
In this context, the main objective of this research was to analyze which aspects related to inclusion and integration favor equal opportunities. A quantitative perspective was adopted as a new aspect, using causal regression models to find out which aspects were or were not significant in favor of equal opportunities. To achieve this objective, a survey was conducted among 133 primary and secondary school teachers and therapeutic pedagogy professionals in Spain.

Inclusive Education and Sustainability
Agenda 2030 [16] considers education a fundamental basis and a privileged tool for making sustainability, inclusion, social justice, equity, and cohesion effective. Education is widely recognized as the essential tool for development, as a means of achieving social welfare, sustainable development, and good governance. Ultimately, education is an essential catalyst for achieving broader development goals and should be at the heart of the global development agenda [16]. There is no more powerful transformative force than education to promote human rights, achieve sustainability, and build a better future for all, based on social justice, international solidarity, and shared responsibility [17].
Despite all of these references linking education to the promotion and development of sustainability, the document that first linked the idea of sustainable development to education was the Delors Report (1996) [18], which placed education as a key vehicle for achieving sustainability goals.
In this sense, the ideals and principles that constitute sustainability include concepts such as equity, peace, tolerance, poverty reduction, and social justice [19]. We can therefore say that equity becomes the core of building an inclusive society [20,21].
In order to carry out any kind of social project based on equity, we must focus on two fundamental concepts: inclusive education and sustainability. Without a guarantee of sustainability, educational inclusion, as with any other principle or value, is meaningless [22]. In this sense, we cannot forget that "a fundamental objective of education is to prepare students and young people for sustainable lifestyles, within sustainable communities and environments locally and globally. Commitment to inclusive values implies a commitment to the well-being of future generations." [23] The issue of inclusive education continues to generate interest and controversy in general among educational professionals, researchers, and politicians, since it ultimately has to do with ideological and political issues that are fundamentally related to the type of world we want and how we understand the terms justice and democracy, among others [22]. In short, the process of educational inclusion is closely related to the general approach from the Sustainable Development Goals, understood as 17 goals to transform the world, to achieve a sustainable future for all, and not to leave anyone behind [17]. Booth and Ainscow [23] argue that all of the values are necessary for the development of inclusive education, yet with sustainability is at the core.
In short, it is necessary to move towards public policies where the promotion of human capital formation can help and assist in the achievement of sustainable development purposes, equality of opportunity, and equity sustained by a state that assumes the role of guarantor of the right to learning opportunities [24]. Moreover, in this horizon, education for sustainability and for inclusion is necessary and even urgent [21,22].

Equal Opportunities: Differences Between Integration and Inclusion
The movements of pedagogical renovation, the advances in educational psychology, and, in short, the evolution of the educational system pay attention for the first time to the diversity of the student body and its schooling, putting the objective of integration through the model of special education [25]. It was not until the publication of the Warnock Report [26], one of the first normrelated texts, that the principle of integration in the school environment was considered. In this way, we directly connected the integration of children with special educational needs into ordinary schools and classrooms.
In truth, the evolution of educational models in western countries has its origin in the global movement of people with disabilities in the 60s and 70s. They recognized the right to education as a key aspect for the achievement of other rights. This aspect goes from gaining strength with the development of key documents, such as the convention against the discrimination of this right (1960), to the evolution of social, historical, and cultural events and the position of the international community on inclusive education policies [27].
Specifically, the evolution towards the integration model in western countries was due to three fundamental changes: The rethinking of special education because of investigations that considered the effectiveness of special classes, the philosophical attacks on special classes, specifically the labeling and classification of students, and the criticism of minority groups.
Court cases breaking down some of the established practices in special education. Normative development beginning to contemplate that special education should not be the only system to serve students with disabilities in a way that considered their education in the least restrictive environment that, for many, meant the regular class [28].
Integration thus became one of the most important and transcendent phenomena in society and for the development of its individuals [29,30]. Obviously, integration implied a great change in educational practice [31] with advances in the field of learning, as shown by studies such as those carried out by Arnáiz [32] and Echeita [33], which state that social integration is considered an active process for the construction of knowledge. However, the truth is that this educational model was not achieved with total guarantees because discriminatory practices and attitudes towards students were not eradicated. Their capacities continued to be questioned and the results were judged in advance with negative prejudices. This situation contributed to the fact that the panorama towards the integration of students into the general curriculum did not change [34,35].
Educational integration suffers from having been based much more on personal prejudices and ideological assumptions than on study and research results [36]. The problems in many of the studies that have advocated integration are found in the methodology, with serious design problems, sample bias, and insufficient and poorly analyzed instrumentation. In addition, this lack of scientific basis possibly explains the difficulties still encountered after four decades of experimentation, without a definitive close to the debate [37].
Currently, integration is outdated and insufficient, as stated in the normative documents, international conventions and recommendations, as well as the most current bibliography. Following the Salamanca declaration [38], educational inclusion has been accepted as orthodoxy in many parts of the world and political responses are evident throughout Europe (e.g., European Agency for the Development of Education for Special Needs). Thus, despite difficulties in interpreting the term "inclusion", all activities must become inclusive [39]. This approach recognizes differences and eliminates barriers to achieving a more egalitarian society in a changing world, thus establishing the basis of the social model [25] which, according to Palacios [40], Shakespeare [41], and Oliver [42], is one that considers that the causes of disability are neither religious nor scientific, but are largely social. The inclusive model is based on the intrinsic foundations and values of human rights in terms of freedom, equality, non-discrimination, etc. This is the background to the need for a new pedagogical model based on normative precepts, such as the Universal Declaration of Human Rights [43] or the Convention on the Rights of the Child [2], among others. Nevertheless, these were reinforced at the UNESCO International Forum in Thailand [44], together with the World Conference on Special Needs Education: Access and Quality [38], which adopted the Salamanca declaration, where we began to speak timidly of inclusion and of education for all. This aspect is currently reinforced by UNESCO [17] with the development of Agenda 2030 for Sustainable Development, the main objectives of which are the creation of more inclusive and equitable societies (SDG 16), starting with inclusive education systems, an aspect that is stated in SDG 4.
Despite this, the implementation of inclusion is problematic within and between educational systems, as well as in northern and southern countries. In northern countries, despite the differences in their definition, their effectiveness is closely related to student management. In southern countries, the meaning of inclusive education is located in the social and political identities of economic development. These issues recognize the controversial nature of inclusive education policies and practices in the international context [45].
Inclusive education has become a 'global-minded movement' [27], at the forefront of the international education policy agenda. There is, therefore, a paradigm shift, a transition from integration to inclusion, as it is the latter that can guarantee the equality of opportunity.
Ainscow [46] understands that inclusion means inserting the student in a space of socialization and learning, propitiating educational interaction and participation in the process of the construction of knowledge; from difference to propitiate learning.
Essentially, inclusion is the realization that every child, adolescent, and young person is of equal concern to the education system. This concern has to do with guaranteeing equitable and quality learning conditions, processes, and results for all [24].
In short, inclusive education is based on the idea of student diversity in all its aspects and considers that the education system should be adapted to each student [47]. Therefore, it is necessary to avoid falling into the widespread error that inclusion only refers to the education of students with disabilities. Inclusive education and attention to diversity does not refer to how a special group of students is educated, but how all of them are educated [48].
The model of inclusion is beginning to take hold at the expense of the integrator, with some lines of argument of various kinds, such as those cited below. For Gento [49], the term "inclusion" has a broader scope and goes beyond integration, because, in addition to encompassing curricular and pedagogical aspects, it incorporates those of a social and physical nature. According to Bello and Sánchez-Teruel [50], "inclusion" is a term that is intended to replace the concept of integration, since they consider that inclusion also refers to basic human rights issues that were not covered by integration. On the other hand, inclusion is considered for all students and members of the community, so it has been superseded by integration and goes beyond that, changing the attitude and conception [51]. However, authors such as Torres [52] understand that the new model of inclusive school is related to integration, although it presents differences with respect to this and therefore understands that integration can be considered a stretch on the road to inclusion. If we focus on the approach based on addressing needs, Parrilla [8] considers that, in integration, the needs are those of the students and a set of actions is adopted to address them and thus ensure that they are adapted to an ordinary school, quite the opposite of the inclusive approach. As Arnáiz [53] and Moriña-Díez [54] rightly point out, the differences between inclusion and integration lie in aspects such as the fact that the integrative school focuses on diagnosis, while the inclusive school focuses on collaborative problem-solving.
In short, the inclusion movement introduces a strong critique of the deficit approach implicit in school integration practices, considering that, in educational practice, integration, in turn, generates processes of segregation even when these may have been considered more subtle. Undoubtedly, with the emergence of the inclusive model, we are facing a new transformation in the school reality-a process of the ideological and conceptual rearmament of the approaches to school integration [52].
In recent years, it has become necessary to address diversity in order to make one of its basic principles a reality: opportunity and equality for all-that is, a school for all [55]. Inclusive education is education that is based on the paradigm of offering equal educational opportunities to all those involved in the educational process [56].
Given this analysis, we can conclude that the right to education encompasses the right to an inclusive education, since it is established as a mechanism to guarantee human rights, equal opportunities, and justice [57]. The implementation of educational inclusion involves working on issues such as social justice and equal opportunities [58][59][60]. This aspect is reinforced in the PISA 2015 report, which refers to two fundamental pillars for responding to equity: equal opportunities and educational inclusion.
In summary, we must affirm that the educational model, which makes it possible to manage with equity and to really attend to the diversity of the student body and where the student body with disabilities has real equal opportunities, must be inclusive. Therefore, implementing and practicing an inclusive model in schools requires a global rethinking of the education system, since is based on and justified by some antagonistic principles, typical of a selective model [12] and, in our opinion, still focused on the integration model.
Based on the review and previous literature to date, the following research questions are intended to be answered: Q1: Do inclusion measures, policies, and knowledge favor equal opportunities? Q2: Do integration measures and policies have a negative effect on ensuring equal opportunities?

Related Works
Inclusive education has become the cornerstone of many government policies in a growing number of countries, yet teachers have been found to have conflicting attitudes towards its implementation and usefulness [61]. Therefore, tools must be available to facilitate the improvement and implementation of an inclusive education system [62].
The results of the research by Duhan and Devarakonda [63] demonstrated a change in the conceptualization of inclusion in different areas, one of them being related to equal opportunities and rights, although in a lesser percentage and importance. Likewise, other works, such as Qu [63], highlight the need for teachers, in this case in China, to analyze and reflect on what educational equality really means in terms of inclusion, beyond equal treatment.
Teachers are considered key elements in implementing inclusive education [64]. They are concerned about their training and their ability to deal with more inclusive practices [65,66].
Cochran [67] conducted a comparative study between regular and special education teachers in the application of the scale called STATIC (Teachers' Attitudes Toward Inclusive Classroom), finding four components of inclusive education: advantages and disadvantages, training, philosophical aspects, and logistical aspects (resources).
Horne and Timmons [65] conducted both a qualitative and quantitative study on teacher attitudes where they concluded that one of the main concerns of teachers was the continuous professional development needed to respond effectively to the increasingly diverse needs of students in the classroom.
Vaz et al. [68] applied the ORI scale (Opinions Relative to Integration of Students with Disabilities), developed by Antonak [69], and found an important finding demonstrating the importance of teachers' knowledge to improve inclusion.
The study by Vanderpuye, Obosu and Nishimuko [70] investigated the attitudes of teachers and their perceptions of the resources they need for the effective implementation of inclusive education.
Their findings recommended, among other things, that to sustain the practice of inclusive education, teachers' needs must be met. These include information on special needs and disabilities, training on how to effectively teach students with special educational needs, training on the adaptation of materials, and guidance and recommendations on how to promote social interaction. Ultimately, teachers must be educated, trained, and informed about all aspects of educational inclusion.
In relation to the knowledge of disability and inclusion of teachers, the results provided by Kamenopoulou and Dukpa [71] expose these aspects as deficient and contrary to inclusion, showing a lack of knowledge and teacher training as an obstacle for the implementation of educational inclusion.
If we focus on teachers' disability knowledge, the results reveal the need for more training and education in the subject [72,73]. This is also the case for teachers at specific stages, such as the early childhood stage [74], as teacher training on disability is low, as opposed to knowledge on inclusive teaching methods, which is acceptable [75] but not sufficient or appropriate as it translates into a barrier to their development [76]. Although research, such as that of Thomas and Uthaman [77], has shown that there is a significant correlation between teachers' knowledge and their attitudes towards inclusion.
The effective teaching profession is considered a priority in education policy. A teacher who understands diversity, is inclusive, and continues to be trained demonstrates some of the basic components that all teachers must incorporate to be promoters of inclusive, equitable, and quality education for all. This is an important element within the new education agenda of 2015-2030 [20].
However, no studies have been found in the literature that validate scales of what components should make up an inclusive system; that is, which aspects should be established and developed to guarantee inclusive education from the point of view of teachers, such as, their opinions or assessments of the components that currently make up the system [78]. Moreover, this aspect has not received special attention in the literature. In this sense, therefore, a measure of the dimensions that make up inclusive education has not been validated. No attempt has been made to measure all the components of inclusive education and, above all, to carry out causal studies to determine which ones are more important for achieving inclusive education.
Based on this, the following research questions were established: Q3: Does the training and knowledge of teachers influence the promotion of equal opportunities?
Q4: What are the real measures to promote equal opportunities from the point of view of teachers?

Sample and Field Work
For the development of this study, we took the teachers of Obligatory Secondary Education and professionals of therapeutic pedagogy in the Autonomous Community of Andalusia as a population. To obtain the sample, we used a non-probabilistic snowball sample. The fieldwork was carried out during January 2016.
Thus, we were faced with a population of nearly 9000 teachers in the target region of analysis from which we finally obtained a sample of 133 subjects with a sampling error of 3.7% with a 95% confidence rate. A total of 142 responses were obtained, but after a debugging process, responses that were completed in less than five minutes were eliminated (the average time was 10 minutes). Likewise, those responses in which response patterns were found and those with the same response in all questions were deleted. The characteristics of the sample are detailed below, where it stands out that 60% of the respondents claimed to have medium/high knowledge about the field of disability, while 20.2% claimed to know hardly anything about this field. On the other hand, almost 65% of the sample was made up of women and almost 65% of the sample were professionals who worked in public education centers (see Table 1). Source: own elaboration.

Instrument
To carry out our study we used a questionnaire as a data collection technique with a total of 53 items. This was a self-administered online questionnaire. The questionnaire consisted of two parts: (1) classification of the surveyed persons and sociodemographic variables (sex, age, center, etc.); (2) a total of 40 Likert-type scale questions (from 1 to 5) regarding three fundamental aspects: knowledge about disability, consideration, and the effectiveness of measures of attention to diversity, opinion, and information on inclusion (see Appendix A).
As for the measures of the variables, no scales for measuring the inclusion of the education systems have been found recently, which is an important novelty of this work. Some studies, such as those of Wilczenski [79], Sharma, Forlin, and Loreman [80], or Humphrey and Symes [81] measured teachers' attitudes towards students with disabilities, an objective that differs from our aim of developing a broad vision of all the components of inclusion.
For this reason, an ad-hoc scale was developed which included various aspects related to inclusion in relation to previous literature. To validate the content of the scale, a group of experts, specifically 10 teachers of Didactics and School Organization from several Andalusian universities with extensive experience in the evaluation of questionnaires, were consulted. As a novelty, the scale included the assessment of educational transit programs for people with disabilities in order to prevent them from dropping out of school.
A pre-test was carried out during the year 2015. The results of the survey were analyzed by 26 teachers with more than 20 years of experience working in public schools. With the results found, the correct elaboration and understanding was again verified, correcting the errors detected. In addition, content validity and reliability were checked with a Crohnbach's alpha value of more than 0.7 (0.803). It was also checked through the method of the two halves obtained-for the first part a value of 0.887, and for the second part a value of 0.801, which confirms the results obtained previously.

Procedure
Firstly, a factorial analysis was performed, an interdependence method (it does not distinguish between independent and dependent variables) that starts from a large number of variables (in our case, the 40 Likert-items of the questionnaire) to treat whether they have a small number of factors in common that explain and summarize the starting information, thus simplifying the relationship between the items. In summary, it groups observable variables to form new so-called factors from the combinations of the previous ones [82].
Secondly, a confirmatory factor analysis was carried out, the objective of which was to validate the results found regarding the constructs of the exploratory analysis to confirm the dimensions. Confirmatory factor analysis is a tool used to confirm or reject measurement theory [83]; in our case, the values.
In third and last place, multiple regression models were carried out. The regression deals with the study of the dependency of a variable to be explained with respect to some explanatory variables, trying to determine the structure or form of the relationship; that is, the mathematical equation that relates the independent variables to the dependent one [82]. In this way, we wanted to check how the relationship of the dimensions of inclusion and integration is with the dependent variable to be analyzed, equal opportunities.

Exploration and Reduction in Dimensions
In order to understand and compare how the dimensions included in the questionnaire were structured, an exploratory factorial analysis was carried out to understand how the items related to educational inclusion behaved (40 total). The analysis offered adequate values of KMO (0.71) and Barlett's sphericity test (p=0.00) was favorable for the analysis. The communities, that is to say, the representation of the different items of the questionnaire within the factorial analysis exceeded, in all cases, the minimum value of 0.5, with the exception of the item referred to the "specific classroom schooling modality" (0.459). However, it was decided that the value should be maintained since it was close to 0.5 and would not affect the factorial solution given the very good results achieved in both the goodness of fit and communality analyses.
A total number of eight factors was selected, given the criterion of choosing self-values greater than 1 and according to the Kaiser test. These factors accounted for 64.8% of the total variance explained. Then, a rotation phase was carried out using the Varimax procedure to find out the structure of the eight factors. This rotation was used because it is an orthogonal method and because it is one of the most widely used approaches, as highlighted by Luque-Martínez [83]. The results do not vary when other orthogonal rotation methods are used, such as Quartimax or Equimax.
A total of eight dimensions were obtainedm which were as follows: (1) measures for attention to diversity; (2) measures of integration; (3) adaptation to an inclusive system; (4) curricular modifications; (5) teaching training; (6) knowledge of disability; (7) knowledge of inclusion; (8) student integration. This scale offers a Cronbach's alpha value of 0.90, which confirms the first previous reliability of the dimensions achieved.

Confirmatory Factor Analysis
A confirmatory factorial analysis was then performed through the PLS program [84] for the possible debugging of the scale. In order to check the validity and reliability of the constructs, a second-order confirmatory model was made, consisting of all the items that make up the proposed dimensional scale.
After measuring the proposed eight-factor scale, five of the items did not have the appropriate psychometric properties: the first item referred to disability knowledge (the modality of schooling in a specific classroom at an ordinary center encourages integration), another item related to student integration measures (the existing measures for attention to diversity really do respond to student diversity), another one related to teachers (the establishment of measures of attention to diversity is the consequence of the lack of integration of our students), and two related to the adaptation to an inclusive system (students with special educational needs do not have to attend school in a specific classroom; assessment of Special Educational Needs (SEN) implies the access of the student with SEN to a special education center). For the remaining items, loads were significant (p < 0.01) and higher than 0.7 [85]. Cronbach's alpha, composite reliability (CR), and mean extracted variance (AVE) values were above acceptable cut-off levels (0.7, 0.8, and 0.5, respectively) [86,87]. It can therefore be concluded that the scales used had good psychometric properties in all cases, as shown in Table 2.
On the other hand, discriminant validity was tested by applying the procedure proposed by Fornell and Lacker [88] by which the square root of the variances extracted must be greater than the correlations between the constructs, shown in Table 3. The criterion suggested by Henseler et al. [87] was also applied through the heterotrait-monotrait ratio of the correlations (HTMT). The HTMT is an estimate of the correlation of the factors (more precisely, of an upper limit). In order to clearly discriminate between two factors, the HTMT must be significantly smaller than 1, as shown in Table  4.
Finally, the adjustment model had adequate indices and the mean residual standardized square root (SRMR) was 0.08; an adequate value as it was lower than 0.10 [87]. The NFI value was 0.67 (less than 0.90).

Explanatory Model for Equal Opportunities Through Inclusion
The factors obtained in the previous section allowed us the possibility of carrying out a causal model that explains different aspects related to inclusion. This allowed us to know in a parsimonious and clear way which were those dimensions that correlated in a stronger way with certain key points of the equality of opportunities. Such an explanatory model is carried out through the multiple regression technique that, in our case, was carried out through the linear regression method. Therefore, the main objective was to establish an explanatory causal linear regression model of equal opportunities. To this end, the eight dimensions obtained in the factorial solution after debugging the scale when performing confirmatory factor analysis were included and are detailed in Figure 1. The dependent variable was the item that measured the perception of how inclusive education promotes equal opportunities (measured on a scale of 1 to 5). All factors included are related to capacities and measures to improve inclusion in education. This is a complete and comprehensive model of the explanatory or causal variables that lead to improved equality of opportunity.
The linear regression model was significant through the ANOVA test (P = 0.000; F = 5.452) and in this case the r-square obtained was 32%, so it had an acceptable and sufficient explanatory capacity.
In the model, the necessary conditions of normality of the residues, the existence of heteroscedasticity, as well as multicollinearity, achieved favorable results for the interpretation of the coefficients estimated in the model.
Observing Table 5, in the p-value column (p = 0.000), it is indicated that, with a 95% confidence level, it is possible to check which values are significant in our linear regression model and which are not.
The order of importance of the explanatory or independent variables was deduced from the "Beta" column. Thus, the explanatory variable that acquired less weight was the integration of students (−0.189) while the one that explained more was the knowledge about inclusion (0.360).
In addition, in the column of parameters B, the coefficients of variation that occured in the dependent variable when faced with the unitary variation of some of the variables can be observed, assuming that the rest of the variables remained constant. Thus, according to the results, any increase in certain explanatory variables would increase the equality of opportunity. For example, improving knowledge about inclusion by one unit would increase it by 0.360. Some of the relationships between independent variables and the dependent variable were negative (for example, carrying out integration measures), so that any action in any of the aspects would reduce equal opportunities.
In -Integration measures were an aspect that has no significant impact (p = 0.302) on improving equal opportunities in the education system. However, the most relevant aspect was that it has a negative impact (Beta= −0.093). This is a highly relevant result since it implies that integration does not promote equal opportunities. It follows that the effective mechanism is inclusion. Different schooling, according to the psycho-pedagogical evaluation of the student, or the integration measures that are appropriate for students with disabilities are some of these measures.
-Adapting the education system to inclusion was the second most important aspect.
Eliminating special education centers to promote ordinary centers, reducing specific centers or enrolling students with disabilities in ordinary centers were fundamental measures for ensuring equal opportunities in a significant way (p = 0.000).
-Curricular modifications did not have a statistically significant impact. However, it had a positive effect on equality (0.042). In this case, the factor included two aspects: the psychopedagogical evaluation, an element that benefits equality of opportunity, and the same referred to curricular adaptations. This led to the conclusion that inclusion can be an objective where the agents involved and awareness raising become more important than school measures.
-Nor did teaching training have a significant impact (p = 0.109). Again, there was a positive relationship. Having a prepared teaching staff, improving their training, and promoting equal opportunities are aspects that increase equality in a positive way between students, whether they have a disability or not.
-Knowledge of disability also had a positive, though not significant, effect (p = 0.678).
-As might be expected, knowledge of inclusion was the main element in shaping an inclusive education system (B = 0.360). Significantly (p = 0.000), improving the information and knowledge of all agents in the social and educational system would enable greater levels of equality of opportunity to be achieved.
-Finally, favoring the integration of students was an aspect that had a negative impact on equal opportunities (B = −0.189) in a significant way (with a confidence level of 90%) (p = 0.052). Specific or integrative classrooms and schools are measures that reduce equality.
Thus, it is true only inclusion that really allows it. (2)

Discussion
The aim of this study was to find out what aspects shape and explain the promotion of and increase in equal opportunities in education. To this end, we have answered the following research questions: Firstly, we have answered our first research question about how inclusion promotes equal opportunities. As the results of our research and the analyzed literature show, there is no doubt that inclusion is the educational model based on the paradigm of offering equal educational opportunities to all those involved in the educational process [55]. The implementation of educational inclusion implies working on issues such as social justice and equal opportunities [57,58,59]. UNESCO [7] states that inclusion is a movement to transform education systems to realize the right to education with equal opportunities.
The results of our research highlight the importance of adapting the education system to inclusion, eliminating specific centers to ensure equal opportunities. This reaffirms the idea put forward by Rodríguez [89], that special education has historically conceived of diversity as a countervalue and as a division of society into categories. This idea of restricted and reductionist diversity being characteristic of special education must be overcome to introduce a broader and more inclusive meaning [32]. Inclusive education questions the creation of specialized services or differentiated measures based on previously defined categories [90]. Special education versus inclusive education approaches need to address changes and modifications. Special education as a parallel educational system to that provided to the majority has been challenged by ideas of inclusion, in which it is considered that all children should be part of the same educational system [91].
Secondly, the following research question has also been answered in relation to the negative effect of the integration model on ensuring equal opportunities. This is an aspect that can be seen in the previous answers: in the results of our research; in what has been exposed by the international community through its sustainable development goals [17]; in what is reaffirmed with the analysis of the literature that understands in this sense that the term inclusion has a greater scope and goes beyond integration [49] among other issues because it addresses the human rights issues that integration does not include [50]. Educational integration and its measures suffer from having been based much more on personal prejudices and ideological assumptions than on study and research results [36]. Research linking the medical model of disability with the integrative school model explains the difficulties of the integrative model. This aspect refers to issues such as the definition it provides of people with disabilities as unable to guarantee the needs of normal social life due to a deficiency [27]. The results of our study show that integration measures have a negative impact on improving equal opportunities. The analyzed literature supports this issue by recognizing that integration is currently outdated, and the objectives of education required are specified in the inclusion of all students to achieve a more egalitarian society according to the bases of the social model [25]. Our quantitative results extend the qualitative research carried out by Schmidt and Venet (2019) [92], which analyzed the differences between inclusive education and the integration of students with learning needs. The physical integration of students with learning disabilities into the regular classroom should be extended to inclusive philosophy and practice, as integration is insufficient. In the end, the results obtained assume that integration does not promote equality of opportunity and therefore derives from these results, as supported by previous studies. The concept, practice, and attitudes that relate to integration are overcome by inclusion [51]. It has pedagogical approaches that are contrary to inclusion [8,52,53]. In short, the inclusive model involves a new transformation of the reality of schooling and a process of ideological and the conceptual rearmament of the approaches to school integration [9] in order to make the basic principles of opportunity and equality for all a reality. In other words, a school for all [54]. Inclusive education is education that is based on the paradigm of offering equal educational opportunities to all persons involved in the educational process [55]. Equal opportunities in an inclusive education system imply the elimination of barriers to learning, accessible environments and universal accessibility. In short, inclusion is the possibility for each student to reach his/her maximum potential in education.
Thirdly, if we focus on the third research question about teacher training and equal opportunities, teachers are seen as key elements in the implementation of inclusive education [64]. According to research by Schmidt and Venet [92], teachers are an element whose leadership style influences the inclusion achieved in the center. Teachers whose leadership is "reculturing" change the paradigms of integration towards inclusion, which validates the positive results of our study on the fact that teachers can favor equal opportunities. The evidence in our work affirms, as does previous research, that a profound change and reflection is needed in relation to the conceptualization of inclusion and equality of opportunity [62,63]. Research data from Horne and Timmons [65] and Jordan et al. [66] conclude that there is a concern for their inclusive training and practical skills. They are aware of the importance of training and knowledge as a fundamental aspect of inclusive education [67,68]. Specifically, the study by Vanderpuye, Obosu, and Nishimuko [70] highlighted the need for training on special needs, disability, and ultimately training on capacity building and information on all aspects necessary to address educational inclusion [72][73][74]. The importance of awareness of inclusion in the education system supports the results of other studies in other sectors. Research by Greer and Egan [93] showed that increasing knowledge about inclusion among managers in organizations favors human and structural diversity and the career advancement of all employees. In other words, it favors equal opportunity. Training deficiencies in this sense are an obstacle to the implementation of educational inclusion [71].
Consequently, in response to the fourth research question on the main factors for achieving inclusion from the point of view of teachers, they are, in order of relevance: to improve and increase knowledge about what inclusion really is; to increase measures to address the diversity of the student body in order to achieve equity; to adapt equipment, educational policies and learning, according to the principles of inclusion.

Conclusions
The main objective of the present work was to establish the inclusive factors that allow for the improvement and increase in the equality of opportunities through a causal linear regression model.
An important contribution and novelty of this work was the achievement of an empirical causal model that explains the equality of opportunities through aspects related to inclusion, knowing in a clear and concrete way which dimensions correlate in a stronger way with certain key points of an equal opportunities system.
A factorial analysis was carried out in order to reduce the number of items in the questionnaire. With this, a total of eight dimensions were found. The scale was validated and refined through confirmatory factor analysis. From these factors it was deduced that three of them have a positive and significant impact on equal opportunities. In order of importance they are the following: The most important aspect is the factor to have knowledge about inclusion. This means that it is important to really know what inclusion is, how it works, and how it should be applied correctly.
The second aspect is the factor to adapt the education system to a truly inclusive system. All people should be included in ordinary schools, adaptations should be made for all students regardless of their circumstances, and integration measures should be avoided.
Finally, the third aspect in order of relevance for achieving equality is the factor to take and implement measures to address diversity. Changing assessment and learning methodologies or making flexible groupings are aspects to be applied to achieve real equality of opportunity. A novel aspect in our study is that it included the assessment of the importance of carrying out transition programs between different educational stages to avoid the school dropout of people with disabilities.
Although they were not statistically significant, it has been shown adequately that the factors about teaching training and adopting curricular modifications have a positive relationship with equal opportunities.
It has also been shown that there are aspects that have a negative impact. The factor of the integration of students, in a significant way, reduces equality. Although not significant, the factors of school integration measures also have a negative impact. This is a result of notable relevance in our study since it empirically demonstrated that integration is an exclusionary system that does not guarantee equal opportunities. The real effective mechanism is inclusion. The linear regression model demonstrates more than 30% of equal opportunities inclusion. Therefore, a very high value of the reality explained in the area of Social Sciences is reached [94,95].
The results achieved have implications for various agents. In the first place, managers or policymakers must make changes in educational laws regarding inclusion, in accordance with the precepts of the Convention (2006) and the Consolidated Text (2013) [96] and, above all, with sustainable development goal number 4, related to inclusive education. In line with the SDG, it has been demonstrated that an inclusive education system, rather than an integration one, is one that truly promotes equal opportunities.

Limitations
Among the limitations of this study are the fact that the sample reached is limited to the Spanish context, as well as the fact that given the novelty, complexity, evolution, scope, and current situation of inclusion, not all of the variables involved in the process and promotion of equal opportunities may have been included.
Another limitation is that, despite the importance of inclusion in the educational field, the literature is limited in two fundamental aspects: on the one hand, in comparative studies between the model of integration and that of inclusion as guarantors of equal opportunities; on the other hand, in works that relate inclusion as a key aspect to ensure and promote equal opportunities.

Future Research
As future lines of research, it would be of great interest to broaden the international and geographical horizon by carrying out comparative studies, thus achieving a better extrapolation of the results. Although we are aware of the difficulty involved, it is advisable to periodically analyze the level of inclusion and equal opportunities in society in order to compare every year and check the achievement of the objectives and examine the evolution and understanding of the term of inclusion and its consequences.