Math lesson plan · 2nd grade (Year 3 in England) · 45 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 · 5 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.
- Diego collected 23 shells in the morning and 34 in the afternoon. How many is that altogether? → 57Prompt: Add the tens, then add the ones.
- There are 55 balls in a box and 37 on the table. How many balls are there in all? → 92Prompt: Add the tens, then add the ones.
- There are 19 stars in a box and 52 on the table. How many stars are there in all? → 71Prompt: Add the tens, then add the ones.
Hook · 5 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 · 10 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 · 10 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 66 + 26 by using the nearest tens. Which estimate is best? (70 / 130 / 200 / 100) → 100Prompt: 66 is close to 70. 26 is close to 30.
- Ana says 71 + 21 = 92. Use an estimate: is that answer sensible? (Yes / No) → YesPrompt: Round each number to the nearest ten and add.
You do: independent practice · 10 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 · 5 min
- Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
- Kai says 44 + 25 = 69. Use an estimate: is that answer sensible? (Yes / No) → YesPrompt: Round each number to the nearest ten and add.
- Estimate 28 + 25 by using the nearest tens. Which estimate is best? (90 / 160 / 60 / 30) → 60Prompt: 28 is close to 30. 25 is close to 30.
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