Pumpkin Lab teaching notes

For teachers, co-op leaders and parents. One lesson of about forty-five minutes, for ages eight to fourteen, that ends with every student holding a stencil of a face they carved. Two turns follow for classes that want them: the math of where a cut goes, and the science of the face on the wall. Each part says what to say, what students do, what their screens should show, what usually goes wrong, and a question to ask. You do not need to have carved a pumpkin or to code.

Using this with a class? Make a free class and add your students yourself: each gets a username and password, with no email or Google account needed. Or give them one join code. Using Google Classroom? Post the link there; with a free class, the link also puts each student in your class, so you see their work.A first lesson: Everyone carves a face, prints the stencil, and tapes it to a real pumpkin or a paper bag. Before the cutting, each student says which cuts would fall apart on a real pumpkin and why, and fixes those in the lab first.

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About this lesson

One lesson, three parts. Students carve a face on a 3D pumpkin, light it, fix the cuts that would fall apart on a real pumpkin, and print the face as a stencil at its real size. The stencil goes home, or onto a real pumpkin, or onto a paper bag with a tea light in it. The lab is at its best when the thing becomes real afterward.

Everything you are asked to say or point at is written here in the words that are on the screen. The lesson only uses what it has already taught.

Before you start. If real pumpkins are cut, an adult does the cutting, and the stencil says so at the top. The lab's starter faces are plain kinds (classic, happy, scary, a cat, a ghost, a moon, a bat) and it has no gore; keep it that way. The night view draws shadows, which is the heaviest thing the lab does; on a slow Chromebook, keep the brightness down or skip the shadows part.

How to read this guide

  1. Say what to tell the class, in a sentence or two. Use your own words if you like.
  2. Students do the steps, in order. Read them out or put them on the board.
  3. Screens should show what you should see over a shoulder when it is going right.
  4. What goes wrong the usual snags, and what to say.
  5. Ask one question whose answer shows the idea landed.

Part 1: carve a face (15 minutes)

  1. Say A pumpkin is a hollow shell with a light inside. Every cut changes what gets out. You get as many tries as you want.
  2. Students do Open the lab. On the Style bench pick a pumpkin. On the Shape bench move Ribs and Rib depth, then Stem lean, and watch it change. On the Carve bench press a face (Classic face, Happy, Scary, Cat, Ghost, Moon and stars, Bat), then tap one of the marks in the list and drag it on the pumpkin to move it. Press + Shape and tap the pumpkin where it goes. Pick up the Saw and drag across the pumpkin; bring the line back to where it started and watch the piece fall out. Try the Scoop and the Poke.
  3. Screens should show A ribbed pumpkin with a face cut through it, the readout under it saying how many cuts, and the Carve bench listing the marks. A sawn loop leaves a hole with orange flesh showing on its walls.
  4. What goes wrong Dragging turns the pumpkin instead of cutting: a tool has to be picked (Saw, Scoop or Poke) and Turn it puts the tool down. A mark that will not move: tap it in the list first, then drag it. Too many marks: a pumpkin keeps 24; tick the box beside each one to go and press Remove chosen.
  5. Ask What is the difference between a cut that goes through and a shave? (A shave takes the skin off and leaves the flesh, so light shows through without a hole.)

Part 2: light it, then fix what would fall apart (15 minutes)

  1. Say Now we find out what a real pumpkin would do with your face. Two things: whether the light gets out, and whether any piece falls out that should not.
  2. Students do On the Light bench press Night. Press the Back view button to look past the pumpkin at the wall the face lands on. Switch the candle for a tea light or a bulb and pick a color. Then go back to Carve and look for cuts that cut all the way round something: the middle of an O, an A or a D, or a shape inside a shape. Change those to Shave the skin, or move them so they touch another cut and leave a bridge.
  3. Screens should show A dark stage, a flickering candle inside, the eyes and mouth glowing, and the face as light on the wall. Shaved marks glow without a hole. The Carve bench says, under a word cut through, that the middle of an O falls out of a real pumpkin.
  4. What goes wrong Nothing glows: the light is set to No light, or the brightness is down. The face does not land on the wall: it does, on the wall the pumpkin faces; the Back view button looks at it. A slow computer at night: turn off Flickers on the Light bench.
  5. Ask Which of your cuts would fall out of a real pumpkin, and what did you do about it?

Part 3: print the stencil (15 minutes)

  1. Say The lab prints your face at its real size. A 60 millimeter eye is 60 millimeters on the paper. If the face is wider than the paper, it prints on more pages, never smaller.
  2. Students do On the Export bench press A stencil to print, Letter or A4 to match the printer. Open the PDF and read its top line: the pumpkin's width, and what black, gray and an outline mean. Print it. Tape it to a pumpkin or a paper bag, poke along every line with a pin, take the paper off.
  3. Screens should show A one-page PDF for a face on a 30 centimeter pumpkin: black where it cuts through, gray where it shaves, outlines where it only paints, and a line that says a grown-up cuts.
  4. What goes wrong The PDF says nothing to cut: there are no marks, or they are all on the back of the pumpkin; the stencil is the front half. Two pages: the face is wider than the paper (the classic face fits one Letter page and takes two of A4), and the pages join edge to edge at the dashed box.
  5. Ask Why does the lab print the stencil bigger on more pages instead of smaller on one?
What to collect. The stencil, and a sentence from each student about one cut they changed and why. The night picture (Export bench, A night picture) is the design to show a parent.

A math turn: where a cut goes (ages 10 and up, 15 minutes)

A place on a round pumpkin is two numbers: how far round, and how far up. The Carve bench has a box called Carve by code that uses exactly those. Degrees go round from the front, to the right as you look at it; percent up is up the skin from the bottom; millimeters are the size.

  1. Students do On the Carve bench, tick the box beside one mark, press Choose all, then Remove chosen, so the pumpkin is blank. In Carve by code type one line, cut triangle at 20 degrees, 60 percent up, 50 mm, and press Run. Then add the line mirror and run again. Then try cut circle at 0 degrees, 40 percent up, 30 mm and repeat 8 around. Students who know blocks can press Blocks above the box and build the same lines by snapping.
  2. Screens should show One eye to the right of the front; after mirror, its twin to the left; after repeat, a ring of eight holes round the pumpkin, a quarter of the way up.
  3. What goes wrong A red line under the box says what could not be read, by line number: a shape that is not on the list, a percent over 100, a size under 8 or over 300 millimeters.
  4. Ask Mirror turned 20 degrees into minus 20. What would it do to a shape turned 15 degrees? Where would the eighth circle of a ring of eight be if the first is at 0 degrees?

A science turn: the face on the wall (ages 10 and up, 10 minutes)

At night the candle is one small light. Light travels in straight lines, leaves the pumpkin only where there is a hole, and lands on the wall in the shape of the hole, bigger, because the rays spread as they go. That is a shadow cast by a point of light, and it is the same geometry as a pinhole.

  1. Students do Press Night. Move the Brightness slider and watch the wall. Make one eye bigger with its Size slider and watch its patch on the wall grow. Then shave a mark instead of cutting it: it glows, and nothing lands on the wall from it.
  2. Ask Why is the eye on the wall bigger than the eye on the pumpkin? Draw the rays from the candle through the hole to the wall.

More help

About Pumpkin Lab Open Pumpkin Lab

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Page last reviewed October 2026.