L2 Check Answers Using the Inverse

This engaging Year 4 maths lesson on inverse operations helps pupils understand how addition and subtraction are related and how the inverse can be used to check the accuracy of calculations. The lesson builds on prior learning in place value, addition and subtraction, while strengthening pupils’ reasoning and problem-solving skills. The lesson begins with a starter activity that revisits addition and subtraction calculations from previous Year 4 learning. Pupils solve problems using mental strategies or formal written methods and then explore fact families to see how numbers are connected. This recap supports children in recognising the inverse relationship between addition and subtraction. In the main teaching section, pupils are introduced to the idea of using the inverse to check answers. Using a worked example involving a subtraction calculation, children learn how an addition calculation can verify whether the original answer is correct. Through guided discussion, pupils identify errors and explore how inverse operations can help reveal mistakes in calculations. The lesson also includes opportunities for pupils to evaluate when the inverse is the most useful checking strategy, and when other methods such as estimation or place value reasoning may be more efficient. During the independent activity, pupils take on the role of the teacher. They are given a selection of completed calculations and must choose at least five to check. By writing the inverse calculations, they determine whether the original answers are correct or incorrect and explain their reasoning. This task encourages deeper mathematical thinking and supports the development of self-checking strategies. The plenary introduces missing number problems, demonstrating how inverse operations can be particularly helpful when solving equations with unknown values. Pupils practise rewriting problems so that the unknown number appears after the equals sign and use the inverse to find the solution.