Students' attainment in mathematics is associated with several personal and contextual factors, but little research has been carried out to explore the intersectionality between them. The current paper aims to fill this gap. Census assessment data collected in Italy at Grade 10 (on average, 15-year-old students) by the Italian national institute for the evaluation of the educational system were analysed via a multilevel regression model to account for data hierarchy (422,865 students in 24,279 classrooms, in 3,950 schools). Census data in educational research allowed exploration of the intersectionality between independent variables at different levels of the model's hierarchy. Results showed that reading skills mediate the relationship between students' attainment in mathematics and their gender, citizenship status, and socioeconomic status (SES). Implications for policy and practice are discussed.