Lesson 4.3 The Written Method

Steps

1. Warm-up

   Do this: Ask these out loud. Your child answers out loud; no paper needed.

   • Ask: “61 − 30” Listen for: 31
   • Ask: “49 − 20” Listen for: 29
   • Ask: “32 − 10” Listen for: 22
   • Ask: “86 − 60” Listen for: 26
   • Ask: “99 − 80” Listen for: 19
2. Teach the new idea

   Say this: “Line up the places. Start with the ones. If the top digit is smaller, regroup from the tens.”

   Say this: “Cross out the tens digit and write one less above it.”

   Say this: “Standard algorithm: the written method we use every time.”

3. Show how

   Show: 71 − 19 = ___

   Say this: “Ones: 1 is less than 9, so regroup 1 ten as 10 ones. The tens digit becomes 6.”

   Say this: “11 − 9 = 2”

   Say this: “Tens: 6 − 1 = 5”

   Say this: “Check: 52 + 19 = 71”

   Answer: 52

   Show: Sarah sewed 84 stitches and Anna sewed 61. How many fewer stitches did Anna sew?

   

   Say this: “Unknown: the difference.”

   Say this: “Bar model: a long bar of 84 and a short bar of 61; the difference is unknown.”

   Say this: “Equation: 84 − 61 = ?”

   Say this: “84 − 61 = 23”

   Say this: “Answer: Anna sewed 23 fewer stitches.”

   Answer: 23 stitches. Anna sewed 23 fewer stitches.

4. Practice together

   Do this: Your child does these with you. Let them try first; help only after a real try.

   Ask: 82 − 44 = ___

   Listen for: 38

   If stuck: Ones: 2 is less than 4, so regroup 1 ten as 10 ones. The tens digit becomes 7.

   Ask: 90 − 81 = ___

   Listen for: 9

   If stuck: Ones: 0 is less than 1, so regroup 1 ten as 10 ones. The tens digit becomes 8.

   Ask: 64 − 35 = ___

   Listen for: 29

   If stuck: Ones: 4 is less than 5, so regroup 1 ten as 10 ones. The tens digit becomes 5.

   7 more practice items on the lesson page, and on Worksheet A and Worksheet B.

5. Watch for
   • Forgetting to lower the tens digit after regrouping.
6. Game: Snakes and Subtraction

   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.

7. Narration

   Say this: “Tell me what you learned today. Show me with your hands or the counters if you like.”

   Listen for: Subtract with the standard algorithm.

8. Daily habit

   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.

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