Building 2D Shapes

Overview

In this second lesson of the Shape, Space and Measure unit, students construct, compare and describe 2D shapes using sides and vertices. They build on prior learning about recognising common shapes and use mathematical language to explain how shapes are alike and different.

Learning intentions

• WALT construct triangles, quadrilaterals and other polygons.
• WALT identify and count the sides and vertices of 2D shapes.
• WALT compare shapes using mathematical language.
• WALT investigate which shapes can be made with a given number of sides.

Success criteria

• I can build a shape with a chosen number of straight sides.
• I can draw and label triangles, quadrilaterals and other polygons.
• I can count and identify a shape’s sides and vertices.
• I can explain how two shapes are similar or different.

Curriculum links

• Mathematics and Statistics — Mathsteasers: higher-order thinking questions that challenge learners and deepen understanding.
• Mathematics and Statistics — Mathsteasers / Alignment: relevant challenge connected to classroom mathematics content.
• Mathematics and Statistics — Mathsteasers: additional resources for advanced learners.
• Mathematical practices: problem solving, reasoning, communicating mathematical ideas, and selecting and using appropriate tools.

Lesson structure (45 minutes)

1. 0–5 min · Hook and recall. Teacher opens the shape investigation introduction slides and displays a mystery outline made from straight line segments, asking, “How many different shapes could this become if we changed the number of sides?” Students turn and talk, then recall the meanings of side, vertex and polygon. Clarify that a polygon is a closed 2D shape made from straight sides. Briefly revisit that a triangle has three sides and three vertices, while a quadrilateral has four of each.

2. 5–12 min · Model the language. Teacher uses the shape vocabulary and teacher modelling slides to demonstrate building a triangle and a quadrilateral with craft sticks or a geoboard. Model touching and counting each side and vertex once, then compare the shapes using sentence frames: “Both shapes have…”, “A triangle has… but a quadrilateral has…”. Students identify the sides and vertices in several displayed shapes and explain their answers to a partner.

3. 12–27 min · Build and investigate. Teacher places students in five mixed-ability groups of four and gives each group craft sticks, geoboards or elastic bands. Open the group investigation instructions and challenge students to build a triangle, a quadrilateral, a pentagon and another polygon with a different number of sides. Students build, count and check each shape, then record the number of sides and vertices. They investigate: “How many different shapes can you make with four sides?” Encourage groups to alter length, direction and size while keeping the number of sides unchanged.

4. 27–35 min · Compare and communicate. Teacher pauses the activity and invites groups to display one interesting construction. Use the 2D shape property cards as discussion prompts, selecting cards that help students compare properties such as sides and vertices. Students explain one similarity and one difference between two shapes, using terms including polygon, triangle, quadrilateral, pentagon, side and vertex. Address misconceptions, including counting a corner twice or including a curved edge as a side.

5. 35–42 min · Independent record. Teacher distributes the build, draw and label shapes worksheet and refers to the worksheet instructions and example slide. Students draw and label the shapes they built, record the number of sides and vertices, and answer a comparison question. They complete the challenge: “Make or draw two different shapes with the same number of sides. What is the same and what is different?”

6. 42–45 min · Plenary and exit check. Teacher displays the final review and exit question slide and asks students to show or sketch a shape with five sides. Students state its name, number of sides and number of vertices, then share one new observation about shapes. Collect worksheets and note students who need further support with counting or vocabulary.

Resources

• the shape investigation introduction slides
• the build, draw and label shapes worksheet
• the 2D shape property cards
• Craft sticks, ideally in several colours
• Geoboards and elastic bands
• A large demonstration geoboard or magnetic sticks
• Pencils, coloured pencils and rulers
• Shape examples for display
• Five group work spaces

Assessment

• Listen during partner talk and group building for accurate use of side, vertex, polygon, triangle and quadrilateral.
• Check whether students construct closed shapes and correctly count sides and vertices; photograph or record interesting examples if useful.
• Use the worksheet and final sketch to identify students who can construct, label and compare shapes independently.

Differentiation

• Provide shape templates, pre-drawn outlines, larger craft sticks or larger geoboards for students who find fine-motor tasks challenging.
• Use colour-coded sticks or mark a starting point on the shape so students can count sides and vertices systematically.
• Support dyslexic and autistic learners with visual vocabulary, clear one-step instructions, predictable group roles and the option to work beside a trusted peer or independently.
• Offer sentence frames: “This is a ___ because it has ___ sides”; “Both shapes have ___”; “They are different because ___.”
• Extend confident students by asking them to find and draw multiple different shapes with the same number of sides, including irregular examples, and justify why each is still the same type of polygon.