Geometry Progressions Irene, Vince, Renée

Shifts in approaches to content 3D visualization (7th grade plane sections) as a way of understanding volume Big ideas are developed in terms of transformations (instead of congruence)

Differences from current practice congruence described in terms of rigid motions similarity described in terms of transformations similarity, congruence moved to grade 8 (with conceptual introduction in grade 7) plane sections of solids moved to grade 7 students in grade 8 explain proofs of PT & PT converse students in grade 8 explain proof of Triangle Angle Sum Theorem

Surprises! Formulas for volume are given and used in 8th, but the explanation for why they work is a high school topic

Implications for Teaching Using manipulatives and technology will help students understand/visualize similarity, transformations, and congruence Teachers should establish connections to other domains like ratio and proportion, expressions and equations, number system, functions, and statistics and probability High school teachers should plan for some students to have more rigorous experience with big geometry ideas than in the past