Problem-based learning (PBL) as an educational practice continues to have great impact on all levels of education and across different disciplines. The aim of this experimental study is to examine the effects of PBL on prospective teachers' academic achievements and self-regulation. The treatment group (n=36) and the control group (n=21) comprised Middle East Technical University Language Teaching Department senior students attending the Language Testing and Evaluation Course. Quantitative data were collected via an achievement test, an open-ended application exam and a scale on self-regulation in learning. Qualitative data were obtained through student interviews. The quantitative results revealed that PBL was effective for students' knowledge, comprehension and application-level achievements, but it had no significant effects on their self-regulation. The content analysis of student interviews yielded some positive findings about the application of PBL in teacher education, its strengths and weaknesses as experienced during implementation, together with individual and group work processes involved. The study offers some suggestions for the application of PBL in large classes generally and specifically in a teacher education course.