Lesson Study (LS) case studies were conducted in two secondary school teaching practice placements in England. Using Dudley's framework, Geography and Modern Languages trainees and school-based colleagues collaboratively planned a "research lesson". This was taught by the mentor while the trainee and other teachers observed the learning of three "focus" students. The lesson was reviewed and revised for teaching to a parallel group by the trainee and the cycle of observation and evaluation was repeated. In post-lesson study interviews, analysed from a Communities of Practice perspective, mentors claimed that LS facilitated rapid integration of the prospective teacher into departmental working practices while trainees claimed they benefited from the team approach inherent in LS. The process enabled participants to explore collaboratively the "pedagogic black-box" enriching the experience and learning of both trainees and mentors. Successfully integrated, LS improves support for teacher development in teaching practice placements.