Purpose: The research literature in this field demonstrates that instructional leadership provided by principals is essential for student learning, but the question of its impact on students with high and low socioeconomic status (SES) has remained largely unexplored. In the present study, the authors focus on the moderating role of instructional leadership in the relationship between SES and achievement at both the school and student levels. Design/methodology/approach: Using cross-national Programme for International Student Assessment (PISA) 2015 data, the authors fitted multilevel models to investigate whether the effect of instructional leadership on student achievement in math, science and reading varies across groups of students with the different individual as well as school SES levels. Findings: Instructional leadership significantly moderates the relationship between school-level SES and student achievement in math, while the moderation effect for individual SES and instructional leadership is not significant for any subject. Research limitations/implications: This study calls for more research on the moderation role of leadership in the relationship between SES and student achievement, with a specific focus on the integrated models that include the social justice aspect of school leadership. Originality/value: The authors conclude that while instructional leadership might be beneficial in reducing the achievement gaps between schools, it may not make much difference in terms of reducing the disparity between different SES groups within schools.