Among well-being, cognitive, metacognitive and socio-emotional skills, executive functions best explain SES–achievement inequalities

• SES–achievement gaps widen between Grade 6 and Grade 8 in France. • Executive functions are the strongest mediator of SES–achievement inequalities. • Executive functions explain 22% of the total SES–achievement association in Grade 6 and 17% in Grade 8. • Metacognition, socio-emotional skills and well-being show no independent mediation. Socioeconomic disparities in academic achievement intensify during secondary school, yet the mechanisms driving these inequalities remain debated. This study examined whether transversal factors—executive functions, reasoning ability, metacognition and socio-emotional skills—and the related construct of subjective well-being mediate the association between socioeconomic status (SES) and academic performance. Data were drawn from two large, nationally representative cohorts of French students in Grade 6 ( N = 1,684) and Grade 8 ( N = 1,667). Multigroup structural equation modeling revealed that SES predicted academic performance, with gaps widening from Grade 6 to 8. Executive functions consistently emerged as the strongest mediator, accounting for 22% of the total SES–achievement association in Grade 6 and 17% in Grade 8. Reasoning ability also mediated this effect in Grade 6 but not in Grade 8. Metacognition, socio-emotional skills and subjective well-being did not mediate the relation between SES and academic achievement when controlling for all other mediators. Our results indicate that educational inequalities observed in middle school are partly associated with differences in students’ executive functions linked to family SES.