Composite area

Target: Subtract a removed region from a larger rectangle.

Language target: Say whether a region is part of the figure.

Likely miss: Students add a removed region instead of subtracting it.

Ask: Is that rectangle part of the figure or missing from it?

If you see it: Ask whether the missing piece is part of the figure.

Evidence to listen for: The student can show two different decompositions with the same area.

Next: If the areas disagree, one region was counted twice or not at all.

Observable student moves: names both quantities, uses the represented relationship, and revises after feedback. This companion is not a score.