The purpose of this research was to examine physical activity patterns and psychological correlates of physical activity among primary, secondary, and junior college students in Singapore. A sample of 3,333 school students aged 10 to 18 years took part in the study. Results showed that the younger students had significantly higher physical activity levels compared to the older students. In contrast, the older students had significantly higher prevalence of sedentary activity compared to their younger counterparts. Multiple regression analyses showed that the predictors of physical activity intention were different for the three age groups but similar between the two genders. Overall, these findings confirmed the characteristics of physical activity participation in school students and showed that physical activity and sedentary behaviors among students in Singapore were not inversely related to each other. In addition, results also showed that the psychological correlates were different for different age groups. (Contains 5 tables.)