Session 3

Learning targets

I am learning that decomposition means breaking a problem down into smaller parts

I can use decomposition to solve challenges

Decomposition - unplugged


You are going to look at two problems as a class:


Problem one: Organising books

  • This problem is similar to that in the link “BBC Bitesize Second level – What is decomposition?” but instead of organising DVDs, the children will organise books

  • Show the children your collection of books. Ask the children how these books could be organised, for example:

• Using colour

• By size

• Alphabetically by title/author

• By the quality of book cover design

• By the state of the book

  • Decide on a method for organising the books and then sort the books as a class. Get the children to think about the questions they ask during the activity



Problem two: What happens at school on a Wednesday?

  • Explain what happens in school on a Wednesday, the children need to break the question into sections:

• What happens first?

• What time does it start?

• How long until the next activity?

  • Explain that a visual daily timetable is a helpful way to demonstrate this. Model a typical Wednesday on the board

  • Explain that both of these problems were solved by decomposition



  • Model the process of designing and decomposing before the children work independently. Draw around several 2D shapes to create a picture. eg a house or a space shuttle. Then ask the pupils to tell you each of the steps you took to create this picture. Present these as diagrams or drawings

  • Ask pupils to design a picture, drawing around 2D shapes. Give the children a limit on the number of shapes that can be used

  • Give each pupil a copy of the 'Decomposition: step by step' strip sheet

  • Ask the children to break down their design. Draw it in step-by-step stages, so that someone else could recreate it. Remind the children that the more precise and detailed, the better. They may want to include labels, arrows or numbers.


  • Spread the children’s designs out around the room

  • Give each pupil a decomposed version of someone else’s design

  • Ask the children to follow it and to try to recreate the original design

  • The children go around the room to try to find the design which their drawing belongs to. Once the children think that they have found the matching design, they should check with the original pupil that the design and the decomposition are the same