LESSON PLAN

Addition and Subtraction to 1000

Apothem Team

Grade 3 · Computational Fluency

LESSON AT A GLANCE

Warm-up

5 min

Explore

15 min

Consolidate

10 min

Practice

12 min

Exit ticket

3 min

Warm-up

Estimate: 473 + 318. Students jot estimates in 10 seconds. Share. Most should be around 800. Now compute. How close was your estimate? What benchmark did you use?

Explore

Three-strategy challenge: solve 548 - 273 using (1) decompose by place value, (2) add up from 273 to 548 on a number line, (3) compensate (273 is close to 275; 548 - 275 = 273, add back 2). Compare all three strategies: do they give the same answer? Which is fastest?

Consolidate

Practice

Students solve 6 three-digit addition and subtraction problems using at least two different strategies each, showing estimates. Exit ticket: estimate then compute 564 + 278.

Exit ticket

Students solve 6 three-digit addition and subtraction problems using at least two different strategies each, showing estimates. Exit ticket: estimate then compute 564 + 278.

TIP Estimation before computing is a non-negotiable habit. Students who estimate first have a target to aim for and a check to apply. Without estimation, computation is blind.

WORKED EXAMPLES

Walk through 483 + 259 using friendly numbers and compensation.

259 is close to 260 (1 more). 483 + 260 = 743. But I added 1 too many: 743 - 1 = 742. Check: 483 + 259 = 742. Alternatively, decompose: 400+200=600, 80+50=130, 3+9=12. Combine: 600+130+12 = 742.

A student computes 700 - 362 = 462. Is this reasonable?

Estimate: 700 - 400 = 300. The computed answer of 462 is far above 300. It is likely wrong. Recompute: 700 - 362. Add up: 362 to 400 is 38; 400 to 700 is 300. Total: 338. The student likely made an error subtracting from zero.

MATERIALS

•Base-ten blocks

•Open number lines

•Number talk problem display

•Estimation recording sheets

•Hundred chart for pattern checking

WATCH FOR

!Subtracting from zero (e.g., 700 - 362) is the hardest regrouping case. Many students get 462. Use add-up strategy as an alternative that avoids this error entirely.

!Students may add all three digits without considering place value: 473 + 318 = 4+3 + 7+1 + 3+8 = 7+8+11. Reinforce: hundreds add to hundreds, tens to tens, ones to ones.