This study analyzes private tutoring (or extra class) participation and provision in Cambodia using nationally representative data from 138 lower secondary schools. Higher socioeconomic status (SES) students are more likely to have access to feebased extra classes offered by teachers from their same school and are more likely to enroll when offered. But a substantial number of children with an apparent ability to afford extra classes are not participating, which highlights the role of student engagement in explaining enrichment-driven extra class attendance. Higher capacity and better credentialed teachers are more likely to report providing extra classes, and they also earn more than other teachers engaged in tutoring. As a result, the additional income from extra classes is concentrated in a small subset of teachers. There is some evidence that students who do not participate in extra classes suffer additional negative consequences during regular school hours. These different supply and demand elements are brought together into an analysis of student achievement gaps. Not surprisingly, extra classes are associated with higher test scores on standardized tests in mathematics and physics, but these explain only part of the achievement gap between high- and low-SES students. The largest achievement gaps are instead found between students who do and do not take extra classes, which in turn underscores the importance of shadow education research in Cambodia and beyond.