School achievement has long-term consequences for occupational success, mental health, and overall psychological adjustment. The present study examined the association between temperament trajectories from late childhood through adolescence and academic outcomes during late adolescence and young adulthood. Data come from the California Families Project, a longitudinal study of 674 Mexican-origin youth assessed 12 times from Age 10 to 23, and from school records. Results from latent growth curve models indicate that higher levels of Effortful Control (EC) at Age 10 were associated with better academic achievement (i.e., higher high school grade point average and test scores, greater likelihood of high school graduation and college attendance) in late adolescence and young adulthood. Higher levels of Negative Emotionality (NEM) at Age 10 were associated with worse academic achievement, but this effect did not hold for all facets of NEM. Neither the levels nor slopes of Positive Emotionality (Surgency, Affiliation) consistently predicted school achievement. There were no main effects of the EC or NEM slopes; however, statistically significant interactions between these slopes and parental monitoring emerged. When parental monitoring was low, youth who experienced greater increases in EC (vs. flat or decreasing slopes) had better academic achievement, and youth who experienced greater increases in NEM had worse academic achievement; in contrast, when parents closely monitored their children, changes in EC and NEM were only weakly associated with achievement. Overall, these findings demonstrate that temperament in late childhood, and changes in temperament across adolescence, have important prospective effects on academic achievement.