standard_description: Add and subtract within 20, demonstrating fluency for addition and subtraction within 10. Use strategies such as counting on; making ten (e.g., 8 + 6 = 8 + 2 + 4 = 10 + 4 = 14); decomposing a number leading to a ten (e.g., 13 – 4 = 13 – 3 – 1 = 10 – 1 = 9); using the relationship between addition and subtraction (e.g., knowing that 8 + 4 = 12, one knows 12 – 8 = 4); and creating equivalent but easier or known sums (e.g., adding 6 + 7 by creating the known equivalent 6 + 6 + 1 = 12 + 1 = 13).
problem_activity: Stage 3: 20 Cubes
Required Preparation
Materials to Gather
Connecting cubes
Materials to Copy
Blackline Masters
What's Behind My Back Stage 3 Recording Sheet

Narrative
Students work with 20 cubes, organized into two towers of 10 cubes. One partner snaps the towers and puts one part behind their back and shows the other part to their partner. Their partner figures out how many cubes are behind their back. Students record an addition equation with a blank to represent the missing cubes.
Additional Information
Each group of 2 needs 20 connecting cubes.


aligns: no