The Game-Design and Learning (GDL) initiative engages middle school students in the process of game-design in a variety of in-school, after-school, and summer camp settings. The goal of the GDL initiative is to leverage students' interests in games and design to foster their problem-solving and critical reasoning skills. The present study examines the effectiveness of an after-school version of the GDL program using a quasi-experimental design. Students enrolled in the GDL program were guided in the process of designing games aimed at solving problems. Compared to students in a control group who did not attend the program (n = 24), the children who attended the GDL program (n = 20) showed a significant increase in their problem-solving skills. The results provide empirical support for the hypothesis that participation in the GDL program leads to measurable cognitive changes in children’s problem-solving skills. This study bears important implications for educators and theory.