This study sought to investigate what dimensions of didactic-mathematical knowledge preservice teachers discussed when engaged in lesson study and how lesson study supported the preservice teachers in implementing reform-minded teaching of mathematics. We employed an interpretive case study methodology with the intent of conceptualising the lesson study experience of the preservice teachers. The present lesson study took place in methods of teaching mathematics course at a state university in Turkey. We studied the experiences of two cohorts of preservice teachers during two consecutive years. The current study found that the lesson study experience engaged preservice teachers in discussions about the didactical dimension of teacher knowledge and supported their learning to teach from a reform-minded teaching approach.