Math lesson plan · 1st grade (Year 2 in England) · 30 minutes
Subtract by thinking of an addition
Addition and subtraction
CCSS 1.OA.B.4England: Y1 Addition and subtractionEngland: Y2 Addition and subtraction
Objective and success criteria
Students will: Subtract by thinking of an addition.
- I can answer questions on today's skill on my own, without help.
- I can explain each step and say why it works.
- I can check my answer and spot a mistake.
Before and after
Needs first: Add within 20; Subtract within 20
Leads to: Fact families within 20; Story problems: find the missing change; Find a difference by counting up
Materials: Base-ten blocks, Number lines, Hundred square, Mini whiteboards and pens, Printed student sheet (below).
Warm-up · 4 min
- Quick retrieval from earlier learning (Add within 20; Subtract within 20). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- Luis has 11 crayons. A friend gives Luis 6 more. How many crayons does Luis have now? → 17Prompt: Do we join the groups or take away?
- Hana collected 5 shells in the morning and 12 in the afternoon. How many is that altogether? → 17Prompt: Do we join the groups or take away?
- Leo collected 12 beads in the morning and 6 in the afternoon. How many is that altogether? → 18Prompt: Do we join the groups or take away?
Hook · 3 min
- Give a real shopping total or a score difference and ask for a quick estimate first.
- Share the objective: Subtract by thinking of an addition. Read the success criteria together.
I do: model it · 7 min
- Work through the example out loud, saying why you do each step, not just what you do.
- Example: 7 + 7 = 14. Use this to find 14 − 7.
- Step 1: 14 − 7 = 7
- Answer: 7
- Pause after each step and ask a student to say what comes next.
We do: guided practice · 6 min
- Do these together. Students try each step on whiteboards before you reveal it.
- Use the hints as prompts rather than giving the answer.
- 3 + 8 = 11. Use this to find 11 − 3. → 8Prompt: 3 and what make 11?
- To work out 17 − 8, think: 8 + __ = 17 → 9Prompt: Count up from 8 to 17.
You do: independent practice · 7 min
- Students work on the student sheet. Circulate and check the first two answers of every student early.
- Students who finish: write a question of their own for a partner, with the answer.
The 6 questions are on the student sheet below, with answers in the key.
Exit ticket · 3 min
- Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
- Which addition helps you work out 14 − 7? (7 + 7 = 14 / 7 + 14 = 21 / 14 + 7 = 21) → 7 + 7 = 14Prompt: The helpful addition uses the same three numbers.
- To work out 15 − 6, think: 6 + __ = 15 → 9Prompt: Count up from 6 to 15.
Watch out for
- Subtracting the smaller digit from the bigger one in every column (52 − 17 = 45).
- Forgetting to add the regrouped (carried) ten.
Support and stretch
Support
- Review first: Add within 20.
- Use concrete materials: base-ten blocks.
- Give the first step of each question, or a partly worked example to finish.
- Pair with a confident partner for the guided practice.
Stretch
- Move on to: Fact families within 20; Story problems: find the missing change; Find a difference by counting up.
- Explain a common mistake in writing and how to fix it.
- Write a word problem that uses today's skill, then solve a partner's.
Homework and more practice
Free online practice with hints and printable worksheets for this skill: eurekami.com/math/grade-1.
Free lesson plan from eurekami.com/lesson-plan-builder