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CS Lesson 1
Lesson 1 — Understanding decomposition
Lesson 1 — Understanding decomposition
Breaking problems into manageable parts
Breaking problems into manageable parts
Learning intention: Break a familiar task into meaningful subproblems and explain how the parts work together.
Core knowledge for retrieval: Decomposition breaks a complex problem into smaller, manageable subproblems. An algorithm describes precise steps for solving a problem. A dependency means one part needs the result of another part.
Practice and evidence: Create a task map, write instructions for one subproblem, and represent a counting algorithm with a simple flowchart.
Resources: Paper, pens, sticky notes or task cards, and a board or projector.
TASK 1: BREAKING A PROBLEM INTO PARTS · 10 MINUTES
Work with your teacher to break brushing your teeth into smaller jobs.
Write three headings: Preparation, Cleaning and Finishing.
Suggest smaller steps for each part.
Identify what each part produces or achieves.
Choose two steps that must happen in order. Explain why.
Answer: Is use toothpaste a subproblem?
Improve the instruction “clean your teeth” by making it more precise.
Check: Have you named jobs to do, rather than just things you need?
TASK 2: SORT AND EXPLAIN · 15 MINUTES
Work with a partner. Choose tying shoelaces, packing sports equipment or organising a desk.
Break your task into at least three smaller jobs.
Draw a box for each job. Start its name with an action word.
Label each job’s result, also called its output.
Draw an arrow showing where one job needs another job’s output.
Write precise instructions for one job.
Swap with another pair. Follow or trace their instructions and identify one unclear or missing step.
Improve your instructions using their feedback.
Complete: “_____ must happen before _____ because _____.”
Discuss: Why can a simple task need many detailed instructions?
EXIT CHECK · 5 MINUTES
Work independently.
Name two smaller jobs from your Task 2 map.
State the output of one job.
Explain how another job depends on that output.
Complete: “Decomposition helps because…”
Hand in: Your task map, both counting flowcharts, counting traces and exit check.
TASK 3: MAP A COUNTING ALGORITHM · 15 MINUTES
Part A · Draw a flowchart for instructions to say the numbers 1 to 5 in order, then stop.
hint:
hint:
Use ovals for Start and Stop, parallelograms for saying numbers, and arrows to connect them.
Part B · Can you improve this instruction if you were asked to write instructions to count to 1000
hint:
hint:
Use rectangles for setting or changing the number and a diamond for the question. Label its arrows Yes and No.
Trace each chart with your finger. Write down every number it tells you to say.
Check that both produce 1, 2, 3, 4, 5 and do not say 0 or 6.
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