Microteaching Lesson Study [MLS] combines elements of Japanese lesson study and microteaching. A case study of MLS was conducted with 18 prospective teachers in an initial course on learning to teach. Various data sources (i.e., pre- and post-lesson plans, MLS lesson plans, videotaped lessons, transcripts of group discussions, observation field notes, MLS group written reflective reports and feedback surveys) were triangulated. The pre- and post-lesson plans demonstrated growth in participants' knowledge of teaching aligned with an overarching student-learning process goal (i.e., mathematics reasoning). Active learning involving meaningful discussion, planning, and practice, support from a knowledgeable advisor, collaborative deliberation-in-process, and opportunity to trial, analyse and revise were aspects of MLS revealed as centrally important for prospective teacher learning through MLS. (Contains 2 tables and 2 figures.)