# Day 72 — Ten and zero are still ten

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

**Success:** Child partitions ten into two disjoint parts, including 0 and 10, and explains or demonstrates that the whole remains ten when all objects are in one part.

**Prepare:** ten counters, [P03](print-aids.md) 6/4 and [P08](print-aids.md) 0/10, part mat, numeral cards 0 and 10. Fresh check: whole ten, nine in A.

1. **Retrieve, 3 min.** Show yesterday's whole eight with a changed split. Ask, “Did moving objects change the whole?”
2. **Model, 5 min.** Put ten counters into the whole. Move all to B, none to A. Say, “A is empty: zero. B has ten. Together they are the same whole ten.” Recombine and show numeral `10`; do not add another set of ten.
3. **Build and swap, 10 min.** Partners do P08, then P03. They choose a different position for the 0/10 arrangement (A ten/B zero), then recombine. A checker confirms both part spaces plus any spare account for exactly ten; here the spare must be zero. Teacher observes three learners' use of zero as a part.
4. **Fresh check, 4 min.** Give ten new counters; place nine in A. Child places the last in B, says 9 and 1, and returns all ten to whole.
5. **Close, 3 min.** Ask where the ten objects are when A is zero. **Key:** P08 0+10=10 and reversal 10+0=10; P03 6+4=10; fresh 9+1=10.

**If the child treats zero as a missing or forgotten group:** Leave an empty labelled A boundary visibly present and point to the ten objects in B. **Access and record:** Use an empty tactile tray for zero, print/AAC numeral options, a quiet pair and child-directed placement. Record whether the child accounted for all ten independently.