Scale up a thumbnail sketch with AR

Hold up a thumbnail sketch the size of a stamp and a full sheet of blank paper. Ask "How do we get this small idea onto that big sheet without it going lopsided?" Collect guesses. Most students reach for "eyeball it" or "trace it" — name those as real tools, then explain that the tool holds the thumbnail as a see-through layer over the big sheet through the camera, resized to fit, so the drawing hand only has to follow shapes that are already in the right place.

1. (4 min) Students photograph their thumbnail flat and evenly lit, then load it into the tool as the reference image they intend to enlarge.
2. (6 min) Before any AR, students name three proportions in the thumbnail out loud — for example "the head is about a third of the height" or "the wing is twice as long as it is tall." These ratios are what must survive the enlargement, so writing them down turns the enlargement into a checklist.
3. (10 min) Students tape the large sheet down, point the phone at it, and bring up the AR overlay so the thumbnail floats over the surface. They resize the overlay by pinching until it fills the sheet, watching that the aspect ratio stays locked so the shape scales evenly instead of stretching in one direction.
4. (7 min) With the overlay sized, students re-check their three proportions against the enlarged layer. The head should still be a third of the height, the wing still twice as long as tall. If a ratio looks off, the overlay was stretched rather than scaled — reset and pinch again keeping it uniform.
5. (3 min) Quick check: if you doubled the size of the sheet, would the proportions inside the drawing change? Surface the idea that scale changes the size but the ratios stay locked.

• Which three proportions did you name, and why did you pick those over others?
• What is the difference between resizing an image and stretching it, and how did you tell them apart on screen?
• Where do you predict your freehand drawing will drift tomorrow, and how could the overlay catch it early?

Demonstrate propping the phone on a stand so the overlay stays put, then drawing under it. Explain the one rule that makes AR tracing work: keep your head, the phone, and the paper in the same relationship the whole time, because if the camera shifts, the overlay shifts with it. A steady rig turns the phone into a window you can draw through.

1. (6 min) Working in pairs, students set the phone on a stand or book stack above the taped sheet and bring back the resized overlay from session 1, nudging it until it sits square on the large paper.
2. (18 min) The core move: students lightly redraw the sketch by hand, following the overlay one shape at a time — the outline first, then the big interior shapes, saving detail for last. They are told to draw what they see through the camera, not from memory, and to lift the pencil and re-check whenever the phone gets bumped.
3. (6 min) Mid-point check: pull the phone away and look at the paper alone. The enlarged drawing should read as the thumbnail, just bigger. If a shape sits wrong, compare it to the named proportions from session 1 and correct while the lines are still light.

• Where did your enlargement hold proportion best, and where did it drift? Can you trace the drift to a moment the rig moved?
• Did tracing under the overlay teach you anything about the shapes you would have missed drawing freehand?
• Is scaling a sketch up with an overlay any different, honestly, from the grid method your grandparents used? What changed and what stayed the same?

Point students to the how to enlarge a drawing guide and the square-grid method to see how the same proportion idea works with a hand-drawn grid, and to the AR tracing app for how the overlay sits on real paper.