# Day 73 — Find the missing part

**25 minutes · AC9MFN04 · educator review pending**

**Success:** Child starts with a whole up to ten and a visible first part, moves **the remaining original objects** into the second part, and checks by recombining.

**Prepare:** ten counters for [P05](print-aids.md) 7/?/10, seven for P04 2/?/7, part mat and two opaque covers for the second part. Fresh check: whole nine, A two. No written equation is required.

1. **Retrieve, 3 min.** Fill a ten-frame and recall one split from Day 72. Ask how the parts were checked.
2. **Model, 5 min.** Put ten into whole, move seven to A, then move the **three still in whole** to B. Say, “The missing part is what was left of this same whole.” Uncover B and recombine to ten. Briefly show the group of three for accessible visual recognition, then count to verify.
3. **Mystery-part game, 10 min.** Partners use P05 and P04; one moves the given first part, the other predicts or directs the rest into covered B, then both audit by recombining. Teacher asks three focus learners to explain how they avoided taking counters from outside the whole.
4. **Fresh check, 4 min.** Present nine new counters, A already holding two. Child moves the remaining seven into B and proves the whole is nine.
5. **Close, 3 min.** Ask, “Where did the missing part come from?” **Key:** P05 7 and 3 make 10; P04 2 and 5 make 7; fresh 2 and 7 make 9.

**If the child guesses a part without tracking objects:** Return all counters to whole and physically partition again; accept a count rather than insisting on instant recall. **Access and record:** Use raised/covered trays, large pieces, tactile counting, sign/AAC or directed adult movement. Note whether the child predicted, counted, subitised a small group or needed a mathematical cue.