As reflected by national and supranational institutions (OECD, 2023; UNESCO, 2018), the study of social equity and the role of educational systems in its improvement is of undeniable importance. A core indicator of the quality of an educational system is its capacity to promote equity and social justice among all citizens. This involves how the system, through the comprehensive education of all individuals, fosters social mobility and the equitable redistribution of social goods, mitigating the impact of inherited socio-cultural and economic disadvantages on personal development opportunities. Therefore, beyond achieving high average levels of competence or performance, other significant equity-related goals emerge in our educational systems, such as: (1) limiting academic and socioeconomic segregation, and (2) ensuring equal access to education and its outcomes for all citizens.

In the 1960s and 1970s, the publication of the Coleman Report (Coleman et al., 1966) and the conceptualization of social justice (Bolívar, 2012; Rawls, 1971) became pivotal milestones shaping and framing the study of educational equity (Martínez-Garrido & Murillo, 2016). Indeed, the study of equity has gained prominence within the academic sphere (Figure 1), attaining a significant role in educational research over recent decades (Enchikova et al., 2024; Kyriakides et al., 2020).

Much of the growth observed in educational equity studies over the past 30 years can be attributed to the emergence of international large-scale assessments (ILSAs). These assessments, by including data on student performance alongside a wide range of contextual variables at the student and school levels (Gamazo & Martínez-Abad, 2020; Martínez-Abad et al., 2020), enable the analysis of equity across different educational levels and regions of interest (Appels et al., 2023; Martínez-Abad, Crespi, et al., 2024). In this regard, large-scale assessments such as PISA, TIMSS, and PIRLS play a key role in analyzing the distribution and evolution of educational equity and in identifying approaches to foster it. However, there is no consensus in the literature on appropriate methods for measuring and identifying equity (Enchikova et al., 2024; UNESCO, 2018), hindering the traceability and replicability of studies and, ultimately, the robust advancement of knowledge.

Taking this into account, the EVIDENCE Project focuses on proposing formal indicators for the proper measurement of educational equity and examining how indicators of school segregation and equality of opportunity have evolved across countries participating in PISA from 2000 to 2022.

This presentation will showcase the results of the EVIDENCE project in European countries, highlighting the levels of school segregation, socioeconomic segregation, and equality of opportunity, as well as their evolution over the first 25 years of the 21st century.

Under a positivist research approach with a quantitative focus, secondary data analyses were conducted using the databases provided by the OECD within the framework of the PISA assessments. Given the longitudinal nature of this study, all PISA databases were utilized (a total of 8 cycles), from the first edition in 2000 to the most recent one in 2022. Thus, the study followed a non-experimental cross-sectional research design, employing panel data from the various participating countries across the analyzed cycles. The study population comprised 15–16-year-old students enrolled in the education systems of European countries participating in PISA. In each country, the OECD obtains a representative sample through a two-stage stratified cluster probabilistic sampling with probabilities proportional to size. The variables used to construct the equity indicators are: • Socioeconomic and cultural status (ESCS in PISA): Composed of parental occupation, parental educational attainment, and household resources. • Student's average academic performance in mathematics, reading, and science. The derived equity indicators were defined as follows: • Socioeconomic school segregation: Measure of how heterogeneous schools are regarding the distribution of students' socioeconomic levels. It is calculated using the Intraclass Correlation Coefficient (ICC) of the null multilevel model, with the school level as the level 2 in the model and ESCS as the dependent variable. This indicator reflects the percentage of total ESCS variance explained by the clustering of students in schools. • Academic school segregation: Measure of inter-school heterogeneity based on average performance. It is calculated using the ICC of the null model, but with student performance as the dependent variable. This indicator reflects the percentage of total variance in student performance explained by the clustering of students in schools. • Equality of opportunity: Measure of the relationship between student performance and ESCS in a given system. It is calculated as the coefficient of determination (R2) of the correlation between these two variables. This indicator reflects the percentage of total variance in student performance explained by their ESCS. Once the equity indicators were defined, they were calculated while considering the complex design of PISA. To this end, sampling weights were applied, and the plausible values for performance were handled as recommended in the OECD's technical documentation.

Regarding school segregation, the results show that while socioeconomic segregation levels have remained stable (around 30%) and even slightly increased since 2015, academic segregation levels have been gradually decreasing since 2006. However, these levels remain high: socioeconomic segregation accounts for approximately 30% of the total variance in ESCS, while academic segregation exceeds 40%. Southern European countries, such as Spain and Portugal, stand out for their low levels of segregation and the positive downward trend in recent years for both academic and socioeconomic segregation. These results reflect the positive effects of educational policies implemented to reduce segregation. In relation to equality of opportunity (the association between socioeconomic status and performance), a downward trend was observed during the 2003–2015 period, followed by an upward reversal since 2015. By 2022, inequality levels have returned to those recorded 20 years ago: more than 15% of the total variance in performance can be explained by students' socioeconomic and cultural backgrounds. The Nordic education systems achieve the most favorable levels of equity in terms of equality of opportunity, reflecting the excellent educational efforts made and their commitment to fostering social cohesion and development for all citizens. In conclusion, despite the efforts of many European countries to reduce social and educational segregation, reflected in improved segregation indicators within their educational systems, there is still work to be done in some nations. The outlook for equality of opportunity is even less promising. Evidence shows that education systems have failed to reduce the educational gap linked to socioeconomic background, highlighting the importance of developing actions and policies that enhance the functioning of social mobility and reinforce the crucial role of education systems as guarantors of equal opportunities and social inclusion.

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