Math lesson plan · 2nd grade (Year 3 in England) · 30 minutes
Spot the mistake in a written calculation
Addition and subtraction
CCSS 2.NBT.B.9England: Y2 Addition and subtractionEngland: Y3 Addition and subtraction
Objective and success criteria
Students will: Spot the mistake in a written calculation.
- 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 two-digit numbers with regrouping; Subtract two-digit numbers with regrouping
Leads to: the next skill in this area.
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 two-digit numbers with regrouping; Subtract two-digit numbers with regrouping). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- There are 39 balls in a box and 42 on the table. How many balls are there in all? → 81Prompt: Add the tens, then add the ones.
- Ben collected 56 shells in the morning and 19 in the afternoon. How many is that altogether? → 75Prompt: Add the tens, then add the ones.
- Elena has 29 beads. A friend gives Elena 53 more. How many beads does Elena have now? → 82Prompt: Add the tens, then add the ones.
Hook · 3 min
- Give a real shopping total or a score difference and ask for a quick estimate first.
- Share the objective: Spot the mistake in a written calculation. 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: Luis worked out 16 + 28 = 34. What is the correct answer?
- Step 1: 6 + 8 = 14
- Step 2: 30 + 14 = 44
- Answer: 44
- 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.
- Chloe worked out 49 + 37 = 76. What is the correct answer? → 86Prompt: What is 9 + 7? Is it more than 9?
- Arjun worked out 91 − 33 = 62 by doing 3 − 1 in the ones. What is the correct answer? → 58Prompt: You must always take the bottom number away from the top number.
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.
- Tariq worked out 91 − 76 = 25 by doing 6 − 1 in the ones. What is the correct answer? → 15Prompt: You must always take the bottom number away from the top number.
- Chloe worked out 18 + 25 = 33. What is the correct answer? → 43Prompt: What is 8 + 5? Is it more than 9?
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 two-digit numbers with regrouping.
- 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
- 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-2.
Free lesson plan from eurekami.com/lesson-plan-builder