The aim of the present study is to investigate intelligence, self-discipline, interest and motivation as predictors of school achievement. The study is divided into two major parts. The first part is aimed to find the optimal set of predictor variables apart from intelligence. The second part investigates the interaction of intelligence, interest, self-discipline and motivation in a structural equation model. The hypothetical model focuses on the relation between interest and school achievement, which is mediated by intrinsic motivation and on the relation between extrinsic motivation and school achievement, which is moderated by self discipline. A sample of 464 eight graders completed questionnaires of self-discipline, interest, intrinsic and extrinsic motivation, self-efficacy, ability-self-perception, work avoidance and conscientiousness in the fall of 2011. Intelligence test scores were assessed in summer 2011. Hierarchical regression analysis, which were performed for grades in Math, German and English show, that after intelligence, the self concept is the strongest predictor of school achievement. Moreover, conscientiousness, self-efficacy and the identified regulation of extrinsic motivation contribute to the prediction of school achievement. For the second part of the study, which assumes a hypothetical model, the results led the author to modify the supposed paths. Instead of the relation between interest and school achievement, which is mediated by intrinsic motivation, there is now hypothesized a relation between intrinsic motivation and school achievement mediated by interest. Also the relation between extrinsic motivation and school achievement moderated by self-discipline could not be found, so that the relation was replaced by a path from self-discipline to school achievement. Because of the explorative character, the results from both substudies need to be verified with new samples.