Goal: preserve the amount across 99 + 1 = 100 and explain that ten tens make one hundred. Prepare: nine strips, ten singles, a tenth strip, one hundred square/bundle, Day 22 cards.
- Notice, 3: Build 98. Ask for the next two numbers; add one single at a time and leave the loose pile visible.
- Model, 5: At 99 + 1, audit ten loose ones, trade for a tenth full ten, then audit ten full tens and trade them for one hundred square. Show 9 tens + 10 ones = 10 tens = 1 hundred = 100. In each trade, the amount stays equal. Write 100 with zero loose tens and zero ones in the bundled form.
- Guided, 8: Cards A and B show 97 and 99 fictional marks. Learners move 97→98→99→100. Ask at which move the ones trade occurs and why a hundred bundle can replace ten strips.
- Independent, 6: Card C begins with ten full strips. Learner shows the same amount as one hundred square and as numeral 100, then identifies the number immediately before it. Do not require a fine-motor-heavy drawing of 100 dots.
- Exit, 3: Show nine strips and ten loose marks. Ask for the total before and after both trades. Key: 100 in all three arrangements. If “ninety-ten” remains, audit the ten loose and ten full groups physically.