Problem-based learning (PBL) is one of the active learning models that supports flexibility and creativity in learning, and takes individual differences into consideration. The basic principle of PBL is to make students come face-to-face with conditions that could be similar to real ones in their professions. This objective is accomplished by teachers' constructing the problem systematically, and by lessons that allow students to solve the problem individually. This study examined the effect of PBL (the independent variable) on achievement (the dependent variable). Results indicated that PBL increased student achievement levels, with a significant difference between pretest and posttest results. (Contains 4 tables.)