Abstract

In education, relative age refers to the difference in months, within a cohort of entry into the education system. This difference depends on the enrollment cut-off date set by each education system. In Spain, this difference follows the calendar year, meaning that students born in January are considered relatively older, while those born in December are considered relatively younger. Various studies have shown that the effects of relative age can be observed in students’ academic performance, motor development, and socio-emotional development. These differences can last a lifetime. To provide further empirical evidence, this study analyzes the probability of obtaining low scores in the competencies assessed by Program for International Student Assessment (PISA) 2018 in Spain, focusing on students’ relative age, gender, and socioeconomic status. The sample consists of 35,943 students. The results show that relatively younger students have a significantly higher probability of obtaining low scores in all competencies (30%–55%). Gender differences are also observed: females have a lower probability of low scores in science, reading, and overall performance (12%–57%) but a higher probability in mathematics (8%). In addition, a higher socioeconomic level is associated with a lower probability of low scores (72%–94%). These results suggest that the month of birth has a direct influence on the academic performance of students in Spain, which could be due to differences in cognitive and emotional development as a result of immaturity at different stages of development. The results regarding gender and socioeconomic status align with previous research, where females tend to perform better in reading-related tasks but worse in STEM fields. Finally, this study highlights the crucial importance of socioeconomic status in the academic performance of Spanish students.