Addition and Subtraction within 20 — Year 1 Lesson Plan
National Curriculum: Mathematics — Number: addition and subtraction within 20, Year 1
Overview
Pupils develop fluency in addition and subtraction facts within 20, exploring efficient mental strategies including counting on, using number bonds, and the relationship between addition and subtraction. They connect concrete representations to abstract number sentences.
Learning Objectives
- Add and subtract numbers within 20 using practical resources.
- Use counting-on and counting-back strategies efficiently.
- Use known number bonds to 10 to derive facts within 20.
- Understand the inverse relationship between addition and subtraction.
Key Vocabulary
Suggested Lesson Structure
Number bond warm-up: teacher calls a number, pupils show the missing bond to 10 on fingers. Extend: 'If 6 + 4 = 10, what is 16 + 4?'
Model adding within 20 by counting on from the larger number using a number line. Show how known bonds to 10 help: 14 + 3 = 10 + 4 + 3 = 10 + 7 = 17. Model subtraction by counting back. Introduce the inverse: if 12 + 5 = 17, then 17 − 5 = 12.
Pupils use a number line to add and subtract within 20. Then complete a family of four number sentences for a given set of three numbers (e.g. 6, 8, 14: 6+8=14, 8+6=14, 14−6=8, 14−8=6).
Differentiated: fluency (addition and subtraction calculations within 20), then reasoning ('I add 5 to a number and get 13. What was my number?').
Display a number sentence: 15 − □ = 8. How do pupils find the missing number? Share strategies — counting on, using addition as inverse. Reinforce flexibility.
Common Misconceptions
- Counting all from 1 rather than counting on from the larger number — model and practise counting on explicitly.
- Not using known bonds to 10 to bridge — show how 9 + 6 = 10 + 5 = 15 (make 10 strategy).
Prior Knowledge
Pupils should already be able to:
- Secure knowledge of number bonds to 10.
- Ability to count forwards and backwards within 20.
- Understanding of addition as combining and subtraction as taking away.
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