Promoting teachers to lead classroom discourse effectively is a relevant topic for teacher professional development worldwide. This study compares the impacts of two teacher professional development programmes that aim to support teachers in their classroom discourse practices. In one programme, an adaptive and practitioner-led approach was applied, while in the other programme, a more specified and direct instructional approach was implemented. In a one-year intervention study, we investigated how both designs affected teacher knowledge about classroom discourse and teacher beliefs. Both programmes were filmed, and the implementation of their design features was video-analysed. The effects on teacher knowledge and beliefs were measured via self-reporting and a knowledge test. The results show no differences in teachers' knowledge acquisition over time. However, the adaptive-to-practice programme was significantly more successful in affecting teacher beliefs. The findings are discussed in light of further research and practical implications for teacher professional development.