L3 Add 3-Digits and 10s Mentally

This Year 3 Autumn term maths lesson provides a complete, structured approach to teaching children how to add tens to 3-digit numbers mentally. Building on earlier learning from Year 2 and the previous addition and subtraction lessons, this resource develops pupils’ understanding of place value and efficient counting strategies. The animated teaching slides model how adding 10 affects only the tens digit, while the ones digit remains the same—unless crossing a hundreds boundary. Children explore counting in 10s from different starting points, recognising patterns on the hundred square, and identifying which digits change in each calculation. The lesson includes a practical activity where pupils combine number cards with base-10 representations to add tens to 3-digit numbers, with optional support using place value counters or number lines. Assessment opportunities are built in throughout: the starter counts in 10s, discussion about place value changes, observation of strategies, and a plenary task involving missing-number problems and reasoning. The resource also provides guidance on common misconceptions such as changing the ones digit when adding tens or reverting to counting in ones. This comprehensive lesson strengthens fluency, builds confidence, and deepens understanding of mental addition within the Year 3 curriculum.