Especially graduates from the German type of school Hauptschule have problems in the transition from the school to their vocational training. In the present study a three-week summer school program for eight graders is evaluated, which wants to support students in different areas to have a successful transition. To do so two questions are raised: 1. Which effect does the summer program have on the mathematics and reading skills of the students? 2. Which effect does the summer program have on the perceived self-efficacy of the students? The results of the pre-post-design show in all areas a significant effect. For the control group only in reading a significant effect could be observed. Over all the results point out that the summer school influences students knowledge especially in mathematics and perceived self-efficacy positive, but the sizes of the effects differ. This will be discussed referring the current research of summer schools.