We investigated how secondary mathematics teachers check student geometry proofs. From video records of geometry teachers checking proofs, we conjectured that teachers have different expectations for details that follow from written statements than for details that are conveyed by diagrams. To test our conjectures, we randomly assigned 44 secondary mathematics teachers to 1 of 3 experiment groups (n & 13, n & 15, n & 16) in which they viewed and rated representations of instructional practice. Participants in each group viewed treatment or control versions of instructional scenarios and rated the appropriateness of the teachers' work in different segments of each scenario. We compared participants' ratings across and within experiment groups. We found that participants rated lower instruction that deviated from what we hypothesized to be their expectations, confirming our hypotheses.
Justin K. Dimmel, College of Education and Human Development, University of Maine, 330 Shibles Hall, Orono, ME 04469; firstname.lastname@example.org
Patricio G. Herbst, School of Education and Department of Mathematics, University of Michigan, 610 E. University Avenue, Ann Arbor, MI 48104; email@example.com