This document discusses lesson study, a form of teacher professional development where teachers collaboratively plan, teach, observe and refine lessons. It notes that the most effective professional learning for changing teaching practice happens over months through collaboration, experimentation in the classroom, and with leadership support. The benefits of lesson study include improved pupil outcomes, new teacher knowledge, and leaders who can facilitate improvement. Teachers learn through motivation, collaboration, building on prior knowledge and being accountable. Lesson study involves iterative cycles of joint lesson planning, teaching, observation and discussion to refine practice. For lesson study to be sustainable, organizations need to enable collaboration and transfer developed knowledge across the system through leadership and opportunities to communicate learning.