This study used the Quality Talk and dialogic teaching approach with a group of secondary school teachers (N = 7) to train their facilitation of dialogical discussions by small groups of students. The study used video and audio analysis to assess the teachers' observable behaviours during these discussions, before and after professional development; for example, types of Quality Talk questions asked. The study also used face-to-face interviews, held before and after the professional development, to investigate the teachers' beliefs about learning through discussion. Results show that although the number of high-quality questions from the teachers did not increase, the quality of the questions students asked of each other did improve, and resulted in extended periods of dialogic spells. Positive developments were found for teachers' beliefs about the use of dialogue to foster deeper thinking with their secondary school-aged students.