We have applied Problem-Based Learning (PBL) on an introductory programming course for several years with positive results. In this paper we present the outcomes and discuss our experiences of applying a modified version of PBL such that needs less tutoring resources and could better be used in large-scale courses, too. PBL has many positive effects on studying: Students report that they liked the social aspect of studying in a group. Generally students appreciated the possibility to be active

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... articipants in a course. On the other hand, group dynamic difficulties, tolerance of uncertainty and demanding studying skills caused problems that were too hard to overcome to some students. In this paper we introduce different versions of PBL, discuss efficiently and inefficiently working PBL groups and present their characters. We also discuss the possible reasons for differently working groups. Finally, we give some suggestions for interventions that might help the PBL groups to work better.