The present study aims to investigate in which areas teachers need Professional Development Activities (PDAs), the barriers that prevent teachers from participating in PDAs, their frequency of participating in collegiality-based PDAs, and the relationship between their views about the effectiveness of PDAs and their professional commitment. The sample of the study comprised 821 teachers working at different grades in public schools. The study draws the following conclusions: The vast majority of teachers were of the opinion that the PDAs they participated in had positive effects. It was found that teachers mostly needed knowledge about the effective use of information technologies in education as well as about subject-specific teaching methods and techniques. It was observed that teachers did not participate sufficiently in collegiality-based PDAs that include peer coaching. Finally, it was found that teachers' perceptions of barriers to their participation in PDAs, their level of need for PDAs, and their frequency of participation in collegiality-based PDAs had a significant effect on their attitudes towards PD.