LESSON PLAN

Addition and Subtraction: Facts to 20 and Strategies to 100

Apothem Team

Grade 2 · 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

Number talk: 48 + 37. Students solve mentally. Collect strategies: decompose tens and ones; friendly numbers; bridging. Record each strategy on the board. Compare: which is fastest? Which is clearest? All correct strategies are valid; flexibility is the goal.

Explore

Strategy stations: (1) Hundred chart: students colour an addition path (e.g., 48 + 37: start at 48, jump +30 to 78, jump +7 to 85). (2) Open number line: record the same problem as jumps. (3) Decompose: 48+37 = (40+30) + (8+7) = 70+15 = 85. All three representations; compare.

Consolidate

Practice

Students solve 6 addition and 4 subtraction problems to 100, recording their strategy for each. Exit ticket: 65 + 28 using any strategy. Write the strategy name and the answer.

Exit ticket

Students solve 6 addition and 4 subtraction problems to 100, recording their strategy for each. Exit ticket: 65 + 28 using any strategy. Write the strategy name and the answer.

TIP The number talk is not about getting the right answer. It is about making mental strategies visible, comparing them, and building a repertoire. A student who shares a wrong strategy is giving you the most valuable information in the room.

WORKED EXAMPLES

Walk through the friendly numbers strategy for 48 + 37.

48 is 2 away from 50. Add 2 to make it friendly: 50 + 37 = 87. But I added 2 extra to 48, so I subtract 2 from the answer: 87 - 2 = 85. Check: 48 + 37 = 85. The key: whatever you add to one number, you subtract from the answer.

73 - 46 using adding up.

Start at 46. Jump to 50: that is 4. Jump to 73: that is 23. Total: 4 + 23 = 27. So 73 - 46 = 27. Check with addition: 46 + 27 = 73. Correct.

MATERIALS

•Hundred charts

•Open number lines (blank strips)

•Base-ten blocks

•Ten-frames (double)

•Number talk problem display

WATCH FOR

!Students who learned column algorithms may resist mental strategies. Explicitly value mental strategies as faster and more flexible for two-digit arithmetic.

!Students may decompose incorrectly: 48 + 37 as (4+3) + (8+7) = 7 + 15 = 22. They forgot the place value of the tens digits. Insist: four tens plus three tens equals seven tens, not four plus three.