Math lesson plan · 3rd grade (Year 4 in England) · 45 minutes
Estimate sums and differences
Addition and subtraction
CCSS 3.OA.D.8CCSS 3.NBT.A.1England: Y3 Addition and subtractionEngland: Y4 Addition and subtraction
Objective and success criteria
Students will: Estimate sums and differences.
- 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: Round to the nearest 10 or 100; Add and subtract within 1000
Leads to: Use rounding to check if an answer is reasonable
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 (Round to the nearest 10 or 100; Add and subtract within 1000). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- What is 10 less than 653? → 643Prompt: Which digit changes when you subtract 10?
- Which number rounds to 80 when rounded to the nearest 10? (81 / 74 / 85) → 81Prompt: Numbers from 75 up to 84 round to 80.
- What is 100 more than 139? → 239Prompt: Which digit changes when you add 100?
Hook · 5 min
- Give a real shopping total or a score difference and ask for a quick estimate first.
- Share the objective: Estimate sums and differences. 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 129 + 529 by rounding each number to the nearest hundred first.
- Step 1: 129 ≈ 100
- Step 2: 529 ≈ 500
- Step 3: 100 + 500 = 600
- Answer: 600
- 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 598 + 233 by rounding each number to the nearest hundred first. → 800Prompt: Round 598 to the nearest 100.
- Isla wants to estimate 674 − 252. Which is the best estimate? (500 / 1400 / 400 / 40) → 400Prompt: Round both numbers to the nearest hundred.
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.
- Hiro wants to estimate 381 + 306. Which is the best estimate? (700 / 1700 / 70 / 600) → 700Prompt: Round both numbers to the nearest hundred.
- Estimate 593 + 262 by rounding each number to the nearest hundred first. → 900Prompt: Round 593 to the nearest 100.
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: Round to the nearest 10 or 100.
- 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
- Move on to: Use rounding to check if an answer is reasonable.
- 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-3.
Free lesson plan from eurekami.com/lesson-plan-builder