What Details Do Teachers Expect From Student Proofs? A Study of Proof Checking in Geometry

The authors investigated how secondary mathematics teachers check student geometry proofs. From video records of geometry teachers checking proofs, they conjectured that teachers have different expectations for details that follow from written statements than for details that are conveyed by diagrams. They found that participants rated lower instruction that deviated from what they hypothesized to be their expectations, confirming their hypotheses.