Graduate teaching assistants (GTAs) who run independent sections for larger lecture courses typically receive insufficient feedback. Course evaluations, already flawed by numerous biases, offer an amalgam of student reactions to lecture and section, even when comments specifically laud or criticize section instructors. Course designs also vary greatly: Some professors meet regularly with their team of GTAs; others delegate to a lead GTA; and many simply let their GTAs do anything that gets students talking. Instead, we advocate a team-orientation approach: Lesson Study. Modifying the use of Lesson Study in science education, in turn adapted from a Japanese approach gaining popularity among K-12 educators, we concentrate on mentoring that emphasizes collaborative learning, rather than likeability surveys. Sections use a common assignment, which facilitates GTA participation in design and evaluation. The team meets in advance to confirm common pedagogical goals and again after sections to debrief. Insights may lead to immediate adaptations in subsequent assignments in the same term or revisions to the original assignment in subsequent semesters. Overall, this approach centers the collective articulation of lesson plan design and delivery through deliberately reflective practices that benefit both faculty members and GTAs.