standard_description: Prove theorems about parallelograms. Theorems include: opposite sides are congruent, opposite angles are congruent, the diagonals of a parallelogram bisect each other, and conversely, rectangles are parallelograms with congruent diagonals.
problem_activity: Stage 1: Any Way
Required Preparation
Materials to Gather
Collections of objects
Materials to Copy
Blackline Masters
Sort and Display Stage 1 Recording Sheet

Narrative
Students sort 10–20 objects into two or three categories and then show how they sorted. Provide students with a group of items that will be interesting for them to work with such as:
pattern blocks
connecting cubes
counters
combination of the blocks, cubes, and counters
sets of books
Students then show their representation to a partner and ask questions that can be answered about their collection of objects.
Additional Information
Create collections of 10–20 objects with up to three attributes by which to sort.


aligns: no