A prospective survey, was conducted to identify predictors of university students' grade point average (GPA) using separate samples of female (N = 472) and male (N = 142) students over 9 months. Big five personality traits and achievement motivation were measured. Correlations show that conscientiousness (C) and achievement motivation explained variation in GPA. Latent variable structural equation modelling showed that the effect of C on GPA is fully mediated by achievement motivation for both female and male students. Invariant factor and structural. mediation models across the female and male groups are also reported. Finally, the mediation model is shown to remain significant after scholastic achievement is controlled. The findings arc, interpreted within the framework of Neo-Socioanalytic theory. Copyright (C) 2009 John Wiley & Sons, Ltd.