Unit Plan 22 (Grade 1 Math): Compose & Decompose 2D Shapes

Focus: Use 2D shapes to compose new figures and decompose composite figures into known shapes; represent with drawings and manipulatives; explain strategies with precision.

Grade Level: 1

Subject Area: Mathematics (Geometry)

Total Unit Duration: 5 sessions (one week), 45–60 minutes per session

I. Introduction

Students build pictures and figures by combining two-dimensional shapes and then break those figures into parts to see the shapes inside. They use pattern blocks, tangrams, drawings, and labels to model their thinking, focusing on clear explanations of how a figure was made or taken apart.

Essential Questions

• How can I combine shapes to make a new shape or picture?
• How can I break apart a figure into known shapes and count them?
• How do drawings, labels, and shape counts help others understand my work?

II. Objectives and Standards

Learning Objectives — Students will be able to:

1. Compose new figures by combining triangles, rectangles, squares, rhombi, hexagons, and circles.
2. Decompose composite figures into known shapes and record shape counts.
3. Create drawings that match a built figure and add labels (shape names and counts).
4. Describe more than one way to make the same figure (flexible composition).
5. Explain solutions using precise vocabulary and clear representations (MP.4, MP.6 threaded).

Standards Alignment — CCSS Grade 1 (threaded across the unit)

• 1.G.2: Compose two-dimensional shapes (and simple three-dimensional shapes) to create a composite shape, and compose new shapes from the composite shape. (Unit emphasis on 2D.)
• Mathematical Practices: MP.4 emphasized (model with mathematics); MP.6 (precision) and MP.7 (look for structure) threaded.

Success Criteria — Student Language

• I can build a new figure by putting shapes together and draw it with labels.
• I can break apart a figure into known shapes and count each type clearly.
• I can show two different ways to make the same figure and explain my choices.