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Day 12 · A complete factor checkYear 6 Maths · T1 W3–4 · Day 12 lesson

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Year 6 / Mathematics / Term 1 / Weeks 03 04

Part of the full two-week lesson sequence. Check the pack guide and taught point before teaching.

Open for this lesson: Pack guide · Sources and materials · Daily routes · Worked swaps · Fresh learner checks · Aids and text routes.

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Teacher copy: This page may include teaching prompts or answer keys. Answer keys in this public library can be viewed by anyone. Give learners a clean prompt, use checks as formative evidence, and change a case locally when prior access matters.

Learner prompts

Code: AC9M6N02. Goal: find factor pairs without skipping one and justify why 23 is prime. Prepare: scratch grid, D12 routes.

  1. Launch · 2 min. Show 18 and ask for two different rectangular row plans.
  2. Model · 5 min. List 18 as 1 × 18, 2 × 9, 3 × 6; stop when the next trial would repeat a pair. For 23, test possible small divisors 2, 3 and 4; none divide evenly, and 5 × 5 > 23, so an unseen factor pair cannot begin at 5 or more. Therefore only 1 × 23 and 23 is prime. “Not obvious” alone is no proof.
  3. Guided · 6 min. Check 20's factor pairs 1 × 20, 2 × 10, 4 × 5; compare 21's 1 × 21, 3 × 7. Learners explain how pairs link to arrays, not only a yes/no label.
  4. Choice · 6 min. D12-A/B/C, using seats, archive trays or a number detective game; check the full pair list or a justified prime decision.
  5. Exit · 4 min. “Why can 23 have no pair 5 × something whole?” Because 5 × 5 already exceeds 23 and the smaller member of any factor pair must be at most the square-root boundary. Accept a concrete pair-table explanation without requiring square-root notation.
  6. Note · 2 min. Record whether the learner tried all needed small divisors and knew when to stop; recheck with a fresh two-digit number.

Home/extension: Draw rectangles for 18/20. Extension: compare how 2 × 11 = 22 and 3 × 8 = 24 flank prime 23 without treating neighbours as proof.

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