The “shadow education” system of private supplementary tutoring has become quite common in East Asian countries nowadays. Based on the data of Programme for International Student Assessment 2012 (PISA 2012), the paper analyzes the influence of shadow education on the mathematical literacy of students of Shanghai, Hong Kong, Japan and Korea by means of a hierarchical linear model, and estimates the net effect of shadow education using the method of reweighting on propensity score matching (RPSM). The following findings are obtained from the study: First, supplementary math tutoring has a significant positive effect on the math score of students, and such an effect is more obvious on Japanese and Korean students than on Hong Kong and Shanghai students; second, attending supplementary math tutoring may narrow the gap between students in learning performance that is caused by the difference in their families’ economic, social and cultural status (ESCS), thus promoting the equality of educational outcomes.