Objective: The present study investigated whether high school grades can predict medical school grades after controlling for the effects of demographics and entrance examination scores.
Material and Method: The authors used hierarchical multiple regression analyses to predict medical school grades of 223 medical students in the 1997 entering class of the Faculty of Medicine Siriraj Hospital, Thailand, using age, gender, entrance examination scores, and high school grades as predictors.
Results: After controlling for demographics and entrance examination scores, high school grades provided significant prediction only for premedical grades. The type of entrance examination that students took and the type of high school curriculum that the students studied were significant predictors of medical school grades in every level.
Conclusion: Measures of cognitive abilities in academic content were good in predicting short-term academic achievement. Long-term academic achievement in the medical school could be better predicted from academic orientation, commitment to the medical study, and demographic traits.

Keywords: Predictive validity, High school grades, Medical school grades