Teacher learning in Lesson Study: What interaction-level discourse analysis revealed about how teachers utilised imagination, tacit knowledge of teaching and fresh evidence of pupils learning, to develop practice knowledge and so enhance their pupils' lea

• LS focus on pupil learning (not teachers) fuels teacher disposition to learn.
• LS group talk in role taps tacit knowledge reserves to improve micro-teaching.
• Case pupils sharpen teacher understanding of proximal development needs.
• LS helps teachers overcome classroom complexity and see pupils afresh.
• Interaction-level discourse analysis of teacher talk makes teacher learning visible.

This research examines what discourse interactions reveal about teacher learning in Lesson Study (LS) contexts as teachers plan and discuss research lessons.LS group members combined social and cultural capital resources and vivid data from research lessons. This created motivating conditions enabling collective access to imagined practice and joint development of micro practices. Improvements in subsequent teaching, and pupils' learning are reported.Iterative, collaborative LS processes enabled teachers to access tacit knowledge resources and remove filters (developed to cope with classroom complexity), unmasking hidden characteristics of pupils. This both challenged and informed teacher beliefs, motivating joint development of enhanced practices.