Parent guide · Grade 2 Math · Unit 4
Lesson 4.1 Subtracting with Blocks
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 with base-ten blocks.
- You need
- Dice
- Blocks or cubes
- Pencil and crayons
- A King James Bible
- Worksheet A · Worksheet B · the lesson page
Steps
Do this: Ask these out loud. Your child answers out loud; no paper needed.
- Ask: “89 − 10” Listen for: 79
- Ask: “88 − 60” Listen for: 28
- Ask: “53 − 30” Listen for: 23
- Ask: “57 − 40” Listen for: 17
- Ask: “42 − 20” Listen for: 22
Say this: “Show the first number only. Take away the ones, then the tens.”
Say this: “If there are not enough ones, trade a ten for ten ones first.”
Say this: “Trade: swap 1 ten rod for 10 ones cubes.”
Show: 46 − 37 = ___
Say this: “Ones: 6 is less than 7, so regroup 1 ten as 10 ones. The tens digit becomes 3.”
Say this: “16 − 7 = 9”
Say this: “Tens: 3 − 3 = 0”
Say this: “Check: 9 + 37 = 46”
Answer: 9
Show: Gideon had 97 men. He sent 85 home. How many men stayed?
Say this: “Unknown: how many are left.”
Say this: “Bar model: the whole is 97; one part is 85; the other part is unknown.”
Say this: “Equation: 97 − 85 = ?”
Say this: “97 − 85 = 12”
Say this: “Answer: 12 men stayed.”
Answer: 12 men. 12 men stayed.
Do this: Your child does these with you. Let them try first; help only after a real try.
Ask: 87 − 57 = ___
Listen for: 30
If stuck: Take away the tens: 87 − 50 = 37
Ask: 57 − 15 = ___
Listen for: 42
If stuck: Take away the tens: 57 − 10 = 47
Ask: 80 − 70 = ___
Listen for: 10
If stuck: Take away the tens: 80 − 70 = 10
7 more practice items on the lesson page, and on Worksheet A and Worksheet B.
- Showing both numbers with blocks. Show only the starting number.
Start at 99. Roll two dice, make a two-digit number and subtract it. Check your partner’s answer by adding. First to go below 10 wins.
Say this: “Tell me what you learned today. Show me with your hands or the counters if you like.”
Listen for: Subtract with base-ten blocks.
What man of you, having an hundred sheep, if he lose one of them, doth not leave the ninety and nine in the wilderness, and go after that which is lost, until he find it?
One hundred take away one leaves ninety-nine. The shepherd counted carefully because every sheep mattered.
One-minute subtraction drill on Fridays. Mental math: take 10 or 20 away from any two-digit number.
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.