Studies on the interface between cognitive ability (intelligence) and personality in the prediction of academic performance have yielded mixed results so far. Especially an interaction between conscientiousness (and its facet achievement striving) and intelligence has been investigated. The hypothesis is that conscientiousness enhances the impact of intelligence on performance. Based on findings supporting the idea of a non-linear relationship between conscientiousness and performance the present study aimed at a clarification of the mixed results. Given such a non-linear relationship, studies investigating a possible moderating effect should pay attention to the performance level. A sample of N = 271 students completed a conscientiousness and an intelligence measure. Moderated regression analyses revealed a moderation for conscientiousness but not its facet achievement striving in the total sample. However, splitting the sample into a low and a high performer group revealed an enhancing effect of achievement striving for low performers and a buffering effect for high performer. Practical as well as theoretical implications are discussed. (Contains 1 figure and 3 tables.)