Parent guide · Grade 1 Math · Unit 3

Lesson 3.2 Think Addition

Written for the parent. Read the Say this lines aloud as they are, or in your own words. Answers for you are marked Listen for.

At a glance

Time: 5 sessions of 20–25 minutes
Goal: Subtract by thinking of the addition fact.
You need: Pencil and crayons
Print: Worksheet A · Worksheet B · the lesson page

Steps

Warm-up
Do this: Ask these out loud. Your child answers out loud; no paper needed.
- Ask: “14 − 8” Listen for: 6
- Ask: “9 − 7” Listen for: 2
- Ask: “11 − 8” Listen for: 3
- Ask: “9 − 4” Listen for: 5
- Ask: “14 − 9” Listen for: 5
Teach the new idea
Say this: “To find 13 − 5, ask: 5 plus what makes 13? Since 5 + 8 = 13, the answer is 8.”
Say this: “Every subtraction fact has an addition partner.”
Say this: “Difference: the answer to a subtraction.”
Show how
Show: 12 − 9 = ___
Say this: “Think addition: 9 + ___ = 12”
Say this: “9 + 3 = 12”
Say this: “So 12 − 9 = 3”
Answer: 3
Show: Sarah sewed 15 stitches and Anna sewed 12. How many fewer stitches did Anna sew?
$comparison bar model$
Say this: “Unknown: the difference.”
Say this: “Bar model: a long bar of 15 and a short bar of 12; the difference is unknown.”
Say this: “Equation: 15 − 12 = ?”
Say this: “15 − 12 = 3”
Say this: “Answer: Anna sewed 3 fewer stitches.”
Answer: 3 stitches. Anna sewed 3 fewer stitches.
Practice together
Do this: Your child does these with you. Let them try first; help only after a real try.
Ask: 12 − 7 = ___
Listen for: 5
If stuck: Think addition: 7 + ___ = 12
Ask: 9 − 8 = ___
Listen for: 1
If stuck: Think addition: 8 + ___ = 9
Ask: 8 − 5 = ___
Listen for: 3
If stuck: Think addition: 5 + ___ = 8
7 more practice items on the lesson page, and on Worksheet A and Worksheet B.
Watch for
- Adding instead of finding the missing part.
Game: Fact Family Houses
Draw a house with three numbers in the roof (like 6, 8, 14). Your child writes all four facts in the windows. Score a point for each correct fact.
Narration
Say this: “Tell me what you learned today. Show me with your hands or the counters if you like.”
Listen for: Subtract by thinking of the addition fact.
Daily habit
Count back from 20 by ones and by twos. Say the subtraction partners of 10 (10 − 1 = 9 …).

Spread over the week

5 sessions of 20–25 minutes. Stop while it is still going well.

Session 1. Warm-up, then teach the new idea (steps 1 and 2).
Session 2. Warm-up again, then show how with the examples.
Session 3. Practice together, then play the game.
Session 4. More practice on the worksheet, and the daily habit.
Session 5. Quick check: narration and a few practice items. Move on when it is mostly right.