Pumpkin Lab: A Stencil That Holds Together
The library is holding a family carving night and needs one stencil that every family can tape to a pumpkin and cut. The brief has three requirements: nothing falls out of the pumpkin except the cuts themselves, the eyes and nose are symmetric, and the stencil prints at its real size on a single sheet of Letter paper. The starter design, a face with BOO across the bottom, fails all three. The O's lose their middles, the eyes do not match, and the word is so wide the stencil takes four pages. Students test the design with the lab's own checks, then fix it through Carve by code, where every cut is a line like cut circle at -25 degrees, 64 percent up, 56 mm. They replace the second eye with the single word mirror, shave the letters so nothing falls out, and work out how small the word must be to fit the page. By the end, students can find a line of symmetry, explain why a closed shape falls out of a stencil, and explain why a real-size print takes more pages rather than a smaller picture.
At a glance
Essential question
How do designers know a design will work in the real world before anyone cuts it?
Objectives
Students will be able to:
- test a design against each requirement of a brief and record which it passes
- explain why a closed shape cut through falls out of a stencil, and fix it
- make a face's eyes and nose symmetric about a vertical line, using mirror, and say why a word cannot be
- explain why a real-size stencil of a wider face needs more pages, and resize it to fit one
Vocabulary
brief, requirement, stencil, line of symmetry, bridge, real size, iterate
Standards
3-5-ETS1-3, MS-ETS1-2, 4.G.A.3
Time and materials
45 minutes, grades 4-8.
- One computer or Chromebook per student or pair, with a mouse or a trackpad
- A projector
- The worksheet and exit ticket, one copy each per student
- The rubric, one copy per student if you grade the project
- Optional: a real pumpkin or a paper bag, tape and a pushpin, to try a stencil for real (an adult does any cutting)
Prep
Make copies of the worksheet and exit ticket. Before class, open mytekdev.com/try/pumpkinlab?lesson=a-stencil-that-holds-together&ref=tpt-pumpkin-2 once on a student computer to check that your school's filter allows it, and run the walkthrough in Before you teach once (about ten minutes). No account is needed. Printing a stencil is optional: the lab says how many pages it takes before anything prints.
Assessment
- Formative: the brief checklist on the worksheet, the questions under What to look for, and the exit ticket (answer key included).
- Summative: the worksheet's before and after checklist, the student's fixed code and the scale explanation, scored with the rubric out of 12.
Technology and privacy
Runs in any browser, Chromebooks included, with nothing to install. The lab draws the pumpkin in 3D; the night view is the heaviest part, so on a slow Chromebook turn Flickers off on the Light bench. Students need no account and no email: the link works signed out, and nothing they make is stored on our server unless they choose to save it to an account. If your school blocks new sites, ask IT to allow mytekdev.com. With no account the stencil still downloads as a PDF; a note above the lab then says keeping a file needs a free account, which only matters for saving it to the student's Files.
What’s included
- A one-page overview: objectives, essential question, vocabulary, standards and assessment
- A ten-minute walkthrough to rehearse before class, and background in plain words for the teacher
- A 45-minute lesson sequence: warm-up, direct instruction, guided practice, independent practice, closure
- Slides for the board: a PowerPoint file that also opens in Google Slides
- A student worksheet with a QR code
- A 3-question exit ticket, two to a page, with an answer key
- A rubric: 3 criteria, 4 levels, scored out of 12
- Differentiation for English learners, students with IEPs or 504 plans, and students who need more support or more challenge
- Cross-curricular extensions, and notes for teaching it in grade 3 and in high school
- Standards: NGSS and Common Core Math
Standards
These standards describe defining and testing a design against criteria and constraints, lines of symmetry, and scale drawings. Students test a stencil against a brief, mirror its eyes, and fit a real-size print to the page.
| Framework | Code | Grades | Standard | How the lesson meets it |
|---|---|---|---|---|
| NGSS | 3-5-ETS1-3 | 3-5 | Plan and carry out fair tests in which variables are controlled and failure points are considered to identify aspects of a model or prototype that can be improved. | Students test the design against each requirement, find where it fails, and change one thing at a time until it passes. |
| NGSS | MS-ETS1-2 | 6-8 | Evaluate competing design solutions using a systematic process to determine how well they meet the criteria and constraints of the problem. | Students test the starter and each changed version against every requirement and record pass or fail with evidence. |
| Common Core Math | 4.G.A.3 | 4 | Recognize a line of symmetry for a two-dimensional figure as a line across the figure such that the figure can be folded along the line into matching parts. Identify line-symmetric figures and draw lines of symmetry. | Students make the face symmetric about the vertical line down the front and check that the eyes match. |
Checked October 2026 against: NGSS Engineering Design, Common Core Geometry, Grade 4.