Goal: maintain quantity across 79 + 1 = 80. Prepare: seven strips, ten ones, eighth strip, Day 17 cards.
- Notice, 3: Give 78 in a concrete model and ask how many more to reach the next full ten. Key: two ones.
- Model, 5: Starting at 79, add one, verify ten ones, exchange to eight full strips. Point to 80 on the chart and write 7 tens + 10 ones = 8 tens + 0 ones.
- Guided, 8: A (theatre seat diagram: seven rows of ten plus seven) and B (drawing archive: seven sleeves of ten plus nine) show 77 and 79. Ask children to model 77→78→79→80 and physically trade at the final move.
- Independent, 6: C (community hall floor-plan drawing: eight blocks of ten place marks) shows 80. Learner makes an equivalent form of seven tens and ten ones and tells a partner, an adult, or a recording sheet what stayed equal.
- Exit, 3: Ask “What is one more than 79? What is one less than 80?” Key: 80; 79. If 710 appears, ask whether 7 and 10 name separate places or pieces to exchange.