Here is a real tissue box, and next to it a drawing of the very same box on dotted paper.
How does flat, dotted paper let us draw a solid box you could pick up? And look at the lines running back into the page: why do they all lean the same way?
Hold up a real cuboid (tissue box, chalk box, anything rectangular) beside the dot-paper drawing on the IWB. Take two or three hands-up answers, no open call-outs.
Listen for anyone who says the side lines lean the same way — that is the whole lesson in one sentence. Revoice it: so the box only looks solid because every side line uses the same slant.
Look at the cuboid on the dot paper.
First comes the front face. That is the side facing you, with its upright lines staying upright and its base lines following the dots. Next come the depth lines: these are the lines that run back into the page along the slanting dots. The way they lean is called the slant. Last, the back corners join up to close the box.
Once the box is closed you can see three faces: the front, the top and the side. Look closely at the depth lines, and be ready to say what stays the same about every one of them.
Use the illustration, or sketch the cuboid edge by edge on the board. Draw the class's eye to the depth lines one at a time, the point they must reach is that every depth line uses the identical slant.
As the box closes, point to each of the three visible faces and name them: front, top, side. Pupils will need those names for the copybook step. Ask before the back joins up: where will those back corners land? Take a prediction, then reveal. Do not tell them the slant rule up front — let the repeated depth lines make it for you.
Now we draw one on the board together. Today we build a 4 wide by 3 tall by 2 deep cuboid, edge by edge. First we draw the front face, 4 wide and 3 tall. Then we draw the depth lines back for a depth of 2. Last we join up the back corners.
While one pupil taps at the board, the rest of us point in the air which way each depth line will lean before it is drawn. Watch that every depth line lands on the same slanting run of dots. Watch too for the top face and the side face appearing as the box closes.
Talk this one through together — pupils take turns at the board and the class agrees or corrects out loud.
Send a pupil up to tap the front-face corners first. Then, for each depth line, ask the class to point (in the air) which way the line will lean before the pupil draws it. The moment to catch is a depth line drawn at the wrong slant — stop, hold it up against the ones already there, and ask does this one match?
As the box closes, name the top and side faces again so the labelling step lands easily. The drawing itself is short, so spend the time on the slant-matching talk, not on the tapping.
On the dot paper in your maths copy, draw a 4 × 3 × 2 cuboid.
Draw the front face first — 4 wide and 3 tall. Then draw the depth lines back along the dots for a depth of 2, keeping every one at the same slant. Finally, join up the back corners.
Label the front face, the top face and the side face.
Walk the room glancing at the depth-line slant and at the three face labels — this is whole-class copybook practice, not marking. The slip to catch is depth lines drawn at different angles; a quiet nod to hold the pencil along the dots is enough.
Now one pupil at the board builds each cuboid to match a target size, and the rest of us predict the size and confirm the answer. We start with the 4 × 3 × 2 box we already know. Then we build a 2 × 2 × 2 cube. Next comes a wider 5 × 2 × 3. Finally we build a 3 × 4 × 2 to check that the front face can be tall or wide.
For each one, the pupil at the board sets the size and presses Check, and the class watches for the match. Four boxes is the full set, but two is a fine place to stop if time is short.
This is the practice round — pupils take turns at the board, check each answer, and the class confirms before moving on.
The cube (2 × 2 × 2) is the one that catches people out: pupils expect a cuboid and are surprised the depth is drawn the same way for a cube. The 5 × 2 × 3 is the wide stretch, ask the class to predict how many dots wide the front face runs before the pupil at the board sets it. Move quickly from box to box — the talk about matching the slant matters more than the tapping itself. Use the ✓ as part of the talk: yes, that matches the target.
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