By using multiple regression and hierarchical linear modeling, this study investigates shadow education across and within national educational systems in order to estimate the effect of educational equity on the relationship between private tutoring and student achievement. Data are from the Programme for International Student Assessment (PISA) 2012 and supplemented by World Bank data. Results indicate students' participation in three types of private tutoring (commercial company, personal, and family tutoring) are negatively related to student achievement in the cross-national sample. Evidence suggests, however, that private tutoring may differently associate with student achievement depending on student- and nation-level educational equity factors and contexts. Finally, the validity of private tutoring as a measure of shadow education is deconstructed given these results.