Evolution of contextual predictors of Spanish students' proficiency levels: a comparative study between PISA 2015 and 2018

The Programme for International Student Assessment (PISA) has been assessing the competency level of 15 -year -old students for more than 20 years, influencing in turn the establishment of educational policies and practices based on its results at the international level. Although its configuration does not allow for the establishment of longitudinal studies, this article proposes the design of a study of trends that makes it possible to assess the evolution of those factors of a socio-demographic nature or educational context that best predict the competency level of students. Through a multilevel regression analysis (hierarchical linear models) with the Spanish sample of the 2015 and 2018 editions of PISA, comprising 65,684 students and 1,873 schools, we observe changes in the contextual predictors of performance in reading comprehension, science and mathematics. The most notable findings are the reduction of the impact of the migratory status of first -generation immigrants, the reduction of the gender gap in STEM subjects (and its increase in reading comprehension) or the reduction of the contextual effect of the average socio-economic level of a school's student body. It concludes with the need for more in-depth analyses, both at the statistical and policy levels, in order to produce more detailed results to clarify which measures are useful for reducing the impact of socioeconomic, demographic and educational contextual factors on the performance of Spanish students.