Private tutoring refers to additional instruction out of school. With its determinants and effects, private tutoring has received increasing attention from scholars over the past decades. Because of the increasing role of school and high-stakes exams, the demand for private tutoring has increased tremendously in Turkey. The purpose of this study is to examine whether private tutoring mediates the effects of socio-economic status (SES) on students' mathematics performance in the country. This study also addresses how this dynamic varies across types of tutoring: one-on-one tutoring versus tutoring in groups. The findings show that private tutoring partially mediates the effect of SES on students' mathematics performance, and that this dynamic varies across different private tutoring services.