The effectiveness of problem based learning (PBL) in terms of increasing student knowledge and
skills has been extensively studied for higher education students and in non-experimental settings.
This paper tests the effectiveness of PBL as an alternative instruction method in secondary
education. In a controlled randomized experiment, we estimate its effect on tested student
attainments, on perceived student attainments, on autonomous and controlled motivation and on
class atmosphere. The outcomes indicate a non-significant negative effect on student achievements,
a non-significant effect on motivation and a significant positive effect on class atmosphere