Year level: 7

Strand: Space

Lesson length: 60 mins

Using a game, students develop an understanding of how a decision tree algorithm works. They apply this understanding to create their own algorithm to classify special quadrilaterals by their properties. Sequentially it is suggested that the ‘Geometric patterns lesson is completed prior to this lesson, as it covers classifying triangles and quadrilaterals.

Celebrity quadrilaterals: algorithms Image

Achievement standard

Students classify polygons according to their features and create an algorithm designed to sort and classify shapes. They represent objects two-dimensionally in different ways, describing the usefulness of these representations.

Content descriptions

Students classify triangles, quadrilaterals and other polygons according to their side and angle properties; identify and reason about relationships. AC9M7SP02

Students design and create algorithms involving a sequence of steps and decisions that will sort and classify sets of shapes according to their attributes, and describe how the algorithms work. AC9M7SP04

General capabilities


  • Understanding geometric properties (Level 4)

Critical and Creative Thinking

  • Draw conclusions and provide reasons (Level 5)
  • Interpret concepts and problems (Level 5)
  • Draw conclusions and provide reasons (Level 5)
  • Create possibilities (Level 5)
  • Put ideas into action (Level 5)
  • Transfer knowledge (Level 5)

Related content

Digital Technologies, Years 7 and 8 (AC9TDI8P05)

The following opportunities for assessment are described below.

  • Use the Observational checklist of students describing, testing and refining their decision tree algorithms to assess if the students have achieved the success criteria. Decision algorithms can be submitted to teacher at the end of the lesson.
  • A digital submission could be a photo of their group’s decision tree algorithm and a brief reflection summary describing how their algorithm works.
  • Differentiation: Quadrilateral properties quiz using the Quadrilaterals worksheet. This would require another 50 minutes of class time to complete.

Key terms for this lesson: polygon, two-dimensional, algorithm, quadrilateral, parallel, parallelogram, trapezium, rhombus, convex, non-convex.

Some students may:

  • have only encountered one orientation of a plane shape, for example, on a poster in the classroom where only regular pentagons are displayed. Provide examples of different orientations.
  • not realise that classification of polygons is inclusive, for example a square is also a rectangle.

What you need:

  • Lesson plan (Word)

  • Teacher's slides (PowerPoint)

  • Quadrilaterals worksheet (Word

  • Rulers, coloured pencils, markers (or whiteboard markers)

  • A3 paper (or whiteboards)