This article first describes the lesson study practices in Hong Kong, with reference to three General Studies lessons taught in three local primary schools. Data on children's understanding of the concept taught was collected through pra-j and post-interviews and questionnaires, part of the action research cycle. Data on teachers' understanding, choice of teaching strategies and the change in their conception of teaching was collected by interviews, teachers' reflection, both before and after the lesson. The data collected are drawn on to highlight challenges to lesson study and to discuss if this kind of practice is a powerful way for teachers to improve themselves.