'Lesson study' is a professional learning approach in which teachers work together to: formulate goals for student learning and long-term development; collaboratively plan a 'research lesson' designed to bring to life these goals; conduct the lesson in a classroom, with one team member teaching and others gathering evidence on student learning and development. They then discuss the evidence gathered during the lesson, using it to improve the lesson, the unit, and instruction more generally. In this article, a lesson study case from a Japanese elementary school is presented.