Increased physical activity (PA) is the relationship with improved cognitive and memory functions of the brain. The physical education (PE) classes held in school comprise a type of PA. However, there is no epidemiological evidence showing a relationship between school performance and the number of PE classes attended per week in adolescent students. Therefore, the purpose of this study is to examine whether the number of PE classes attended per week is related with school performance in Korean adolescent students. In 2009, 75,066 adolescent students from middle school first grade to high school third grade participated in the 5th Korea Youth Risk Behavior Web-based Survey (KYRBWS-V) project. The relationship between school performance and the number of PE classes attended per week was assessed using multivariate logistic regression analysis after adjusting for covariate variables such as gender, age, body mass index, parents' education level, family's economic status, vigorous and moderate PA, and muscle strengthening exercises. The odds ratio (OR) for attending <3 PE classes per week and school performance was 1.125 for good school performance, 1.147 for average school performance, 1.146 for poor school performance, and 1.191 for very poor school performance, when compared to very good school performance. It was concluded that attending ≥3 PE classes per week was positively correlated with improved school performance and that attending <3 PE classes per week was negatively correlated with school performance in Korean adolescent students.