Codes: AC9M2A02, AC9M2N04. Goal: use a known addition fact within 20 to derive related subtraction facts. Prepare: 20 counters and part-part-whole circles.
- Invite · 2 min. Show 8 blue and 5 plain counters. Ask: “How many altogether? How could knowing the total help if some are hidden?”
- Model · 5 min. Move 8 and 5 into a total circle. Count on from 8: 9, 10, 11, 12, 13. Write
8 + 5 = 13, then cover the 5:13 − 8 = 5. Say: “The same 13 counters make both true.” - Guided family · 6 min. With counters show
6 + 7 = 13,7 + 6 = 13,13 − 6 = 7,13 − 7 = 6. Ask which quantity stays whole and which two are parts. Correct the misconception that subtraction always means physically losing objects. - Partner build · 7 min. Pairs choose parts 9 and 4, build 13, and write/tell four related sentences. Swap to 10 and 6 if ready. One partner checks by rebuilding, not by simply agreeing.
- Use it · 3 min. “There were 13 pencils in a pot. Nine are on desks. How many remain in the pot?” Draw all 13 in two parts; answer 4, if the stated total is trusted.
- Check · 2 min. Everyone fills
7 + 5 = 12; 12 − 7 = __and shows the part. Focus learners explain. If they count from zero, next session rehearse count-on or part circles.
Access routes: tactile counters, enlarged sentence strip, speech/AAC, written numbers or object selection. Exact written notation can follow a correct concrete explanation.