The best professional development for teachers focuses on issues they encounter in the classroom. It is collaborative, school-based, learning-focused and supports teachers in solving problems of pedagogy in context. Through lesson study teachers are empowered to make decisions to improve pedagogy, curriculum and assessment based on evidence of the effect of design on learning. Being explicit about the theories of learning underpinning their teaching decisions allows teachers to develop a shared vocabulary for the diagnosis of learning problems, redesign and evaluation of learning situations....