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Topic ladders · Computer Science

Computational Thinking

One topic, four rungs: from Classes 1–3 to Classes 11–12. Start at your own stage, or climb from the bottom. Every rung follows the same six steps: Notice, Guess, Try, Observe, Explain, Ask another question.

Print the family table: all four rungs side by side on one sheet, so everyone at home can find their own rung.

Choose your class stage

Rung 1 · Classes 1–3

Giving Clear Instructions (Algorithms)

Before you start: safety and help

For the grown-up who helps.

  • Act as the "robot" and follow instructions exactly (even if silly).
  • Safety: If the robot is walking, walk slowly in a clear space, and the instruction-giver says "stop" before any wall, step or furniture.

What you need

  • Paper, pencil
  • A simple task area (e.g., stacking blocks, drawing a shape, moving from one place to another)

Child steps

  1. Notice. When we want someone (or a robot) to do something, we must give clear steps.
  2. Guess. Can you tell a friend exactly how to draw a square or build a small tower without showing them?
  3. Try. Write or speak a sequence of instructions for a simple task. Let a friend follow only your words.
  4. Observe. Did the result match what you wanted? Where did the instructions go wrong?
  5. Explain. Fix the unclear steps and try again.
  6. Ask another question. Can you make the instructions shorter but still clear?
For teachers
  • Learning aims: Understand that instructions must be clear, ordered and complete (early algorithm idea).
  • Key vocabulary: instruction, sequence, step, clear, order.
  • Review: Children share one improved set of instructions.

Rung 2 · Classes 4–7

Patterns, Loops and Decisions

Before you start: safety and help

For the grown-up or teacher who helps. Students: read it too, so you know the rules.

  • Help the child test instructions carefully, one step at a time.

What you need

  • Paper, pencil
  • Grid paper or a simple board with squares

Student steps

  1. Notice. Many tasks repeat the same action or need a choice (if something is true, do this).
  2. Guess. How can you write instructions that repeat or that choose different paths?
  3. Try. Write a set of instructions that uses a counted loop ("repeat 4 times: forward 3, turn right") and a simple decision ("if the square is shaded, turn left") to draw a pattern or move through a grid.
  4. Observe. Test the instructions. Count how many lines you saved by using a loop.
  5. Explain. Explain what the loop does and when the decision is used.
  6. Ask another question. Can you add a second decision or a longer repeating pattern?
For teachers
  • Learning aims: Use sequence, repetition and simple selection in instructions; develop computational thinking.
  • Key vocabulary: loop, repeat, if–then, decision, algorithm.
  • Review: Students demonstrate their instructions and explain the loop or decision.

Rung 3 · Classes 8–10

Breaking Problems into Parts (Decomposition) & Flowcharts

Before you start: safety and help

For the grown-up or teacher who helps. Students: read it too, so you know the rules.

  • This is a paper plan only: no real cooking or hot water is needed.
  • Encourage clear symbols (oval for start/end, rectangle for a process, diamond for a decision, parallelogram for input or output).

What you need

  • Paper, pencil
  • A real problem to plan on paper (e.g., making tea, organising a bookshelf, planning a route)

Student steps

  1. Notice. Big problems are easier when broken into smaller parts.
  2. Guess. What are the main steps needed to solve your chosen everyday problem?
  3. Try. Break the problem into smaller sub-problems. Draw a flowchart showing the steps, decisions and repetitions.
  4. Observe. Check whether the flowchart covers all cases and has a clear end. Every decision needs a "yes" and a "no" path.
  5. Explain. Walk someone through your flowchart and justify the decisions.
  6. Ask another question. How would you change the flowchart if a new condition is added?
For teachers
  • Learning aims: Apply decomposition; represent algorithms using flowcharts; use sequence, selection and iteration.
  • Key vocabulary: decomposition, flowchart, process, decision, input, output, iteration.
  • Review: Students present and explain their flowchart.

Rung 4 · Classes 11–12

Designing and Evaluating Algorithms

What you need

  • Paper, pencil, optional computer or pseudocode environment
  • Optional: 16 numbered cards

Student steps

  1. Notice. Different algorithms can solve the same problem with different efficiency or clarity.
  2. Guess / Hypothesise. Choose a problem (searching, sorting, route finding, or a real-life scheduling task) and propose two different approaches.
  3. Try. Write both algorithms in clear pseudocode or structured steps. Test them with sample inputs, including unusual ones (an empty list, one item, the item not there).
  4. Observe. Compare the number of steps, clarity, and correctness. Identify best and worst cases if possible.
  5. Explain. Discuss advantages and limitations of each approach and suggest improvements.
  6. Ask another question. How does the choice of algorithm matter when data becomes very large?
For teachers
  • Learning aims: Design, compare and evaluate algorithms; use pseudocode; discuss efficiency at an introductory level.
  • Worked example for searching: checking one by one (linear search) takes up to n checks; halving each time (binary search) takes about log₂ n checks, but only on a sorted list. For 1,000 items that is up to 1,000 checks against about 10. Sorting first has its own cost, so binary search pays off when you search the same list many times.
  • Review: Students present both algorithms, test results and a reasoned comparison.

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