Show a photo of the school building, or point out a window if the building is visible from the room. Take three hands-up guesses in metres, no open call-outs.

Do not reveal any method yet, and do not hint at shadows. Let the question sit as a genuine puzzle: how do you measure something you can never reach?

Sketch two triangles side by side: 1 m stick casting a 0.6 m shadow, school casting a 6 m shadow. Same shape because the sun is so far away its light hits both at the same slant.

Draw the ratio out: school's shadow is 10 times the stick's, so school is 10 times taller — about 10 m. Pause and have the class check: 0.6 m x 10 = 6 m, 1 m x 10 = 10 m.

Give Method 1 clear primacy — it is the main method. Keep the three cross-checks brief and visually subordinate.

Bricks: a course is about 7 to 8 cm; roughly 140 courses gives 140 x 7 cm = 980 cm = 9.8 m.

Storeys: each about 3 m; count storeys and multiply.

Comparison: a 1.4 m pupil fitting about 7 times gives 1.4 m x 7 = 9.8 m.

Close with the key point, said aloud and underlined: several good estimates landing close together is what lets us trust the height.

Lead the whole class outside at the start of this step — budget the first minute or two for the out-and-back walk and getting everyone settled at the flat sunlit spot.

Outside: stand a known-height stick (use a metre stick, height 1 m) vertically. Chalk-mark the tip of its shadow and the base, then measure that shadow with a tape. Immediately chalk-mark and measure the school's shadow from the wall base to the shadow tip — both measurements must happen at the same moment, so have two pupils marking at once if you can.

On a clipboard or back at the board, work it aloud: stick height ÷ stick shadow = building height ÷ building shadow. So building height = (1 m ÷ stick shadow) × building shadow. Have pupils call out each number before you divide.

If it is cloudy and there are no shadows, switch to the brick-count or storey-count method as the shared worked example instead.

Send groups of four or five to fixed unreachable features (a flagpole, a tall wall face, a basketball hoop, a tree). Each group settles at one main feature and investigates it with two different methods, then makes quick single-method estimates of two others nearby.

Before releasing groups, board the worked pair and walk the three steps once: (1) difference = larger − smaller, (2) 10% of one estimate (use the first or the larger), (3) difference ≤ that 10% amount means they agree. Numbers: 10 m and 9 m, difference 1 m, 10% of 10 m = 1 m, so yes they agree.

Slip to watch: pupils subtracting the wrong way, or finding 10% of the difference instead of 10% of an estimate. Prompt: is your gap smaller than, or about the same as, one-tenth of your height?

Each group records into the copybook table set up earlier. Circulate and prompt: which method suits a flagpole? which suits a brick wall? Push for a different strategy on the second method so the two estimates are a genuine cross-check, not the same sum twice.

Close by asking pupils to write one line in their maths journal: the most surprising height they estimated today and how they found it.