L5 Add 3-Digits and 100s Mentally

This Year 3 maths lesson provides a clear and engaging approach to teaching pupils how to add hundreds to 3-digit numbers mentally. As part of the Autumn term Addition and Subtraction sequence, this lesson builds on earlier work with place value and counting in steps of 100. The starter activity encourages pupils to practise counting in hundreds from different starting numbers, using a ball-passing game to reinforce the pattern that only the hundreds digit changes as each 100 is added. During the introduction, animated teaching slides demonstrate how the hundreds column increases while the tens and ones digits remain the same. The lesson also models the process on a number line, helping children visualise jumps of 100 and recognise the structure of adding hundreds. The practical task allows pupils to work with cut-up addition questions, recording their calculations and using manipulatives such as place value counters, base 10, or number lines if needed. The plenary consolidates understanding through partner discussion, answer-matching activities, and opportunities for pupils to explain how they solved each calculation. The resource highlights common misconceptions—such as incorrectly changing the tens or ones digits—and provides opportunities for teachers to address place value misunderstandings. This lesson strengthens fluency, reasoning, and confidence with adding hundreds mentally.