Numerous studies indicate that intrinsic motivation predicts academic achievement. However, relatively few have examined various subtypes of intrinsic motivation that predict overall achievement, such as motivation for exercise and physical activity. Based upon the 16 basic desires theory of personality, the current study examined the motives of 178 senior high school (gymnasium) students (mean age?=?17.6, range?=?16-20) from Finland, using the Reiss School Motivation Profile. In structural equation models that controlled for gender and age, intellectual curiosity was positively associated with achievement, whereas the family motive was negatively associated with achievement. Boys had a higher intellectual curiosity and a lower family motive than girls. The physical activity motive had a significant negative interaction with intellectual curiosity, such that youth with higher intellectual curiosity had the strongest achievement when their physical activity motive was lower. This suggests that adolescents with a strong desire for exercise may have some difficulty in selective high schools that require rigorous study and long hours of sitting, even when they enjoy learning. Implications for motivational theory, education research, physical education for promoting fitness, and school psychology practice are discussed.