Download this lovely Year 3 What is Perimeter? Reasoning and Problem Solving worksheet to help develop children's understanding of the concept of perimeter. This resource contains reasoning and problem solving style questions that use shapes with lengths identified and square grids with shapes marked out to encourage children reason their answer regarding perimeter or solve a problem. This activity is a great way to discuss perimeter and make real-life connections. Use it as part of your whole class teaching or within small groups. The helpful answer page makes marking a bit easier.