Lesson objective: Understand that angles can be composed and decomposed.

Students bring prior knowledge of angles from 4.G.A.1. This prior knowledge is extended to additive angle measurements as students compose and decompose angles. A conceptual challenge students may encounter is the ability to think of adding and subtracting angles as one does with whole numbers.

The concept is developed through work with a real-world scenario, which allows the opportunity for students to compose and decompose to angles to think about a mathematical problem.

This work helps students deepen their understanding of operations because students are composing larger angles and decomposing into smaller angles.

Students engage in Mathematical Practice 4 (model with mathematics) as they apply operations to the new concept of additive angles.

**Key vocabulary:**

- angle
- compose
- decompose

**Special materials needed:**

- protractor (optional)
- Wikki Stix® (optional)
- AngLegs® (optional)