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Kindergarten · Mathematics · 20 minutes

Shape detectives

Draw a triangle and a rectangle. Shapes have attributes that stay the same when turned.

Mr. S Teaches · Starter mini-lesson · elem-k-shape-detectives

Learning objective

Explain and practice shape detectives using the activity and evidence, then show the reasoning behind an answer.

Gather your materials

  • Paper and pencil
  • Counters, blocks or paper pieces
  • A ruler, clock model or grid when named in the steps

Use the items named in the teaching steps; paper models or adult-prepared photographs can replace physical equipment.

Common Core skill focus

K.G.B.4

Compare shape attributes across sizes and orientations.

Read the official standard ↗

Code and grade verified 2026-11-03. This mini-lesson addresses a selected skill, not the entire standard.

Teach it step by step

  1. Draw a triangle and a rectangle.
  2. Trace and count straight sides and corners.
  3. Turn the paper and recount.
  4. Compare one shared feature and one difference.

Watch, notice, discuss

Video choices for this lesson

2 choices

Preview a video, then choose what fits your learners. “Show to class” opens a larger view; use the player’s play and full-screen controls when you’re ready.

Teacher preview needed. Check the language, level and length before showing. YouTube may show ads or related videos.

After watching

Choose a shape. Describe its sides and corners, then turn it. What stayed the same?

An external player loads only after you choose Preview or Show to class. Playback connects to YouTube. Videos belong to their creators; availability and embedding can change.

Make the thinking visible

Example to work through together

A triangle has 3 sides and 3 corners; a rectangle has 4 of each. Turning either does not change those counts.

Try the starter activity

Draw a triangle and a rectangle. Count sides and corners.

Student practice

Draw a narrow triangle and a wide triangle; explain how both belong to the triangle group.

Quick check for understanding

Does turning a triangle change its side count?

Sample answer and teacher guidance

Sample answer: No; it still has 3 sides.

Listen or look for: Both have 3 straight sides and 3 corners even though their sizes and orientations differ.

Invite the learner to explain, demonstrate, draw or dictate their reasoning. Revisit a teaching step when the explanation is unclear.

Make it work for your learner

A little more support

Provide cutout shapes and mark each counted corner.

An additional challenge

Compare a square with a nonsquare rectangle using sides and corners.