Math lesson plan · 2nd grade (Year 3 in England) · 60 minutes
Estimate to check whether an answer is sensible
Addition and subtraction
CCSS 2.NBT.B.9England: Y3 Addition and subtraction
Objective and success criteria
Students will: Estimate to check whether an answer is sensible.
- 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; Find numbers on a number line to 100
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 · 6 min
- Quick retrieval from earlier learning (Add two-digit numbers with regrouping; Find numbers on a number line to 100). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- There are 35 shells in a box and 40 on the table. How many shells are there in all? → 75Prompt: Add the tens, then add the ones.
- Arjun has 37 shells. A friend gives Arjun 26 more. How many shells does Arjun have now? → 63Prompt: Add the tens, then add the ones.
- Kai collected 25 marbles in the morning and 45 in the afternoon. How many is that altogether? → 70Prompt: Add the tens, then add the ones.
Hook · 6 min
- Give a real shopping total or a score difference and ask for a quick estimate first.
- Share the objective: Estimate to check whether an answer is sensible. Read the success criteria together.
I do: model it · 12 min
- Work through the example out loud, saying why you do each step, not just what you do.
- Example: Estimate 46 + 22 by using the nearest tens. Which estimate is best?
- Step 1: 50 + 20 = 70
- Step 2: 70
- Answer: 70
- Pause after each step and ask a student to say what comes next.
We do: guided practice · 12 min
- Do these together. Students try each step on whiteboards before you reveal it.
- Use the hints as prompts rather than giving the answer.
- Estimate 56 + 29 by using the nearest tens. Which estimate is best? (120 / 60 / 190 / 90) → 90Prompt: 56 is close to 60. 29 is close to 30.
- Priya says 46 + 27 = 73. Use an estimate: is that answer sensible? (Yes / No) → YesPrompt: Round each number to the nearest ten and add.
You do: independent practice · 17 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 8 questions are on the student sheet below, with answers in the key.
Exit ticket · 7 min
- Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
- Estimate 46 + 27 by using the nearest tens. Which estimate is best? (80 / 180 / 110 / 50) → 80Prompt: 46 is close to 50. 27 is close to 30.
- Tariq says 36 + 54 = 90. Use an estimate: is that answer sensible? (Yes / No) → YesPrompt: Round each number to the nearest ten and add.
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