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The tree of missing parts

Grade 5 pupils use a 3D pen to draw four flat PLA frames: two rectangles and two triangles, one of each with a crossbar and one without: and organise them in a tree of questions on paper. Each frame follows the questions to its own leaf, and its answer trace describes its features. Finally, pupils swap the question order and examine what changed.

Age
10–12 years
Length
approx. 45 min
Level
Easy
Where you teach
School
Purpose
Educational
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How to run this session

Stages and timing
  1. Two rectangles in one colour
  2. Two triangles; pen into its stand
  3. First question: Is it a rectangle?
  4. Draw a tree and devise questions
  5. Each part to its own leaf; a puzzle
  6. Swap the questions
  7. How many leaves for three features? Tidy up

What gets built

The pupil organises objects in a tree by successive features and explains why every object reaches one leaf and what changes when the question order is swapped.

What it practises
  • Organising objects in a tree by successive features. Devising questions about one feature with a YES or NO answer.
  • Recording an object’s path through a tree as a description of its features.
  • Comparing trees with swapped question order.
  • Using a 3D pen to draw unambiguous shapes with clear corners and a crossbar joined to the frame.

Success criteria
  • The four PLA frames are clearly different: without prompting, a partner names each: rectangle or triangle, with or without a crossbar.
  • On W2 side 1, every frame reaches its own leaf and its table trace matches its features.
  • On W2 side 2, the pupil identifies which frames changed leaves after swapping questions and records what stayed the same.
  • The pupil records the leaf count for three features and explains why every question has only two answers.

What you need
Filament
PLA
Colours
one colour per set
Also
1.5 m of PLA filament per pupil (one colour per pupil, two different colours in each pair), 3D pen with stand (one per pupil), transparent work mat, W1: 1:1 pattern for four frames (A4 printout from the package, print 100%), W2: double-sided tree sheet (A4 landscape printout from the package), pencil, ruler

Files

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Version fdaa48e7-e8dc-43f7-8573-12b042b91ff7 Updated 2026-10-16

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