Professional development practices remain at the forefront of ways to support teacher learning but are difficult to sustain. We investigate whether and how teachers continued to perform the professional development practice of lesson study in their own schools after participating in a cross-school Lesson Study Professional Learning Network for four years. We found different perceptions of the general idea of lesson study. If the general idea was modified, teachers rarely continued to perform lesson study; if they did, they transformed lesson study in such a way that core elements were removed. When teachers maintained the general idea of lesson study they were more likely to continue to perform lesson study in their own school and to consider the practice useful.