Students learn how to find the perimeter of complex shapes. Learning progresses from counting the distance around the edge to finding missing lengths of composite shapes. More able students write the perimeter of a shape as an algebraic expression.

The start of the lesson recaps finding the perimeter of simple shapes when all lengths are known. In the main students are taught how to find missing lengths in composite shapes to calculate the total perimeter. The plenary challenges students to link perimeter with collecting like terms and simplifying expressions.

**Differentiated Learning Objectives**

- All students should be able to calculate the perimeter of a shape when all lengths are known.
- Most students should be able to calculate the perimeter of a shape by calculating unknown lengths.
- Some students should be able to write the perimeter of a shape as an algebraic expression.