SubjectNest · Year 3 maths · Make it fit, then check
Day 22 · Start at zero, then make it fit
Make a bookmark that fits. Try an estimate first.
Usual communication and wanted help are welcome. Choose one route; rest or finish when useful.
Full session and all three routes · PDF · Full readable session · HTML
Grown-up: full preparation, teaching and three choices
Day 22 · Start at zero, then make it fit
Make a bookmark that fits. Try an estimate first.
Useful purpose: Estimate and measure length with a labelled ruler; distinguish its physical edge from the zero line.
1 · Find the starting point
Revisit cm versus mL. Ask which of two strips looks longer and why; do not assume a child's finger width is a universal centimetre.
2 · Prepare a suitable invitation
Adult offers a checked ruler, paper strip and book or described rectangle. No scissors required: fold or mark a line; adult cuts only if wanted and suitable. Check zero, equal markings and alignment, and independently verify any printed scale before using it as a real tool.
3 · Brief worked model
This MODEL diagram begins at the 5 cm mark and ends at 14 cm. The length is 14 − 5 = 9 cm, not 14 cm. On a real ruler I can start at zero and read the end, or subtract the two end readings. A decorative printed diagram is not a calibrated ruler.
4 · Guided new try
Align a new safe strip with zero and read a whole-centimetre end together. Slide the strip without changing it; ask whether its length changed. Model reading from above rather than an angled view.
5 · Own attempt
Estimate, choose the start and end, then measure or direct a helper. Record unit and reading. If using only the supplied diagram, say so and answer its mathematical question instead.
6 · Observe and respond
Look for zero alignment, correct unit and the distance between end readings. Record who positioned the tool and who chose/read. A supplied subtraction answer is not evidence of physically aligning a ruler.
Specific next teaching
If the child reads only the last number, compare a new strip from 2 to 8 cm with the same strip from 0 to 6 cm. If alignment is secure, compare two own readings and decide whether a strip actually fits.
Pick a route
1 · Bookmark maker
Will it fit this book?
Estimate a familiar book edge, then measure or direct measuring. Fold a strip to the measured length and compare the fit. Keep the real reading instead of forcing the model's answer.
Observe: Unit, start/end and fit agree; label who handled the tool.
Next teaching: Measure a different edge and explain a mismatch before changing the strip.
Evidence boundary: Observed measuring/directing and fit; adult handling recorded.
2 · Broken-start puzzle
How long is the strip?
Use a MODEL start of 3 cm and end of 12 cm. Show 12 − 3 = 9 cm with a number line, gesture, words or jottings; explain why 12 cm counts an unused section.
Observe: 9 cm with a reason about the start.
Next teaching: Use an unrelated diagram from 7 to 16 cm and hide the written equation.
Evidence boundary: Supplied diagram interpretation only.
3 · Two readings, same strip
Did moving it make it longer?
For a MODEL paper tail, reading pair A is 0 to 7 cm and pair B is 4 to 11 cm. Compare both differences and choose one clear measuring instruction for a helper.
Observe: Both lengths 7 cm; a usable alignment instruction.
Next teaching: Invite a real safe alignment attempt if wanted, separately recorded.
Evidence boundary: Comparison and plan; no physical action inferred.