representing algorithms
4 detailed 50-minute lessons with teaching scripts, worked examples, parent guides, and assessment criteria.
Lesson Overview
Total Lessons: 4
Tier: Foundation and Higher
Duration: 50 minutes per lesson (200 minutes total)
Exam Boards: AQA, Edexcel, OCR, Eduqas, CCEA
Tier: Foundation and Higher
Duration: 50 minutes per lesson (200 minutes total)
Exam Boards: AQA, Edexcel, OCR, Eduqas, CCEA
Learning Objectives
- Explain the key ideas of representing algorithms
- Apply representing algorithms to exam-style questions
- Develop independent study skills
- Build cross-topic connections
Prerequisites
- Read the revision notes for representing algorithms first (GCSE Revise summary)
- Key vocab to pre-teach: Pseudo-code, Flowcharts, Decomposition
- Basic skills: reading the summary notes and answering the practice questions there
Materials & Equipment
- Exercise book, coloured pens
- Ruler
- Printed revision notes (link below)
- Internet for videos (see Resources)
Lesson 1: Introduction: representing algorithms
Duration: 50 minutes
Starter Activity (5 minutes)
Quick Recall
Write down everything you already know about representing algorithms. Then check against the key terms: Pseudo-code, Flowcharts, Decomposition. Use a mini-whiteboard or paper.
Main Content (35 minutes)
Parent/Teacher Guide:
Before lesson: Read the script below. Pre-teach key vocab: Pseudo-code, Flowcharts, Decomposition.
If stuck: Re-read the revision notes (link above), then break the content into smaller steps.
Extension: See the Stretch & Challenge ideas in Lesson 4.
Before lesson: Read the script below. Pre-teach key vocab: Pseudo-code, Flowcharts, Decomposition.
If stuck: Re-read the revision notes (link above), then break the content into smaller steps.
Extension: See the Stretch & Challenge ideas in Lesson 4.
Teaching Script (35 mins):
Mins 0-5 - Hook: "Today: representing algorithms. By the end you will be able to answer exam questions on it unaided. It connects to the rest of Computer Science because the ideas here recur across the spec."
Mins 5-20 - Direct Instruction: Work through the core ideas below one at a time; after each, ask your student to explain it back in their own words.
Mins 20-30 - Guided Practice: Model the worked example together, then let your student attempt the first practice question with guidance.
Mins 30-35 - Independent Practice: 2-3 practice questions from Lesson 3 below, with immediate feedback.
Mins 0-5 - Hook: "Today: representing algorithms. By the end you will be able to answer exam questions on it unaided. It connects to the rest of Computer Science because the ideas here recur across the spec."
Mins 5-20 - Direct Instruction: Work through the core ideas below one at a time; after each, ask your student to explain it back in their own words.
Mins 20-30 - Guided Practice: Model the worked example together, then let your student attempt the first practice question with guidance.
Mins 30-35 - Independent Practice: 2-3 practice questions from Lesson 3 below, with immediate feedback.
First Look
Start with the revision notes summary, then attempt: What shape is used in a flowchart to represent a decision?
Plenary (5 minutes)
Check Out
Your student states one thing they learned and one question they still have about representing algorithms.
Lesson 2: Core Concepts: representing algorithms
Duration: 50 minutes
Starter Activity (5 minutes)
Review Previous Lesson
Quick recap: write 3 key points from Lesson 1 on representing algorithms. Check them against the notes below.
Main Content (35 minutes)
Definition: An algorithm is a step-by-step set of instructions that solves a specific problem. It must be finite, unambiguous, and produce a correct result for all valid inputs.
Pseudo-code: is not a real programming language. It uses structured English with programming constructs to describe algorithms without worrying about syntax rules.
Flowcharts: use standard symbols to represent different types of operations in an algorithm. Each symbol has a specific meaning.
Decomposition: means breaking down a complex problem into smaller, more manageable sub-problems. Each sub-problem can be solved independently and then combined to solve the original problem.
Abstraction: means removing unnecessary detail from a problem so you can focus on what matters. You include only the essential information needed to solve the problem and ignore everything else.
Every algorithm: can be analysed in terms of its inputs (what goes in), processing (what happens to it), and outputs (what comes out). Identifying these is the first step in designing any algorithm.
| Term | Meaning | Example |
|---|---|---|
| Assignment | variable ← value | Store a value in a variable |
| Input | INPUT prompt, variable | Get data from the user |
| Output | OUTPUT expression | Display data to the user |
| Selection | IF...THEN...ELSE...ENDIF | Make a decision |
| Counted loop | FOR...TO...NEXT | Repeat a set number of times |
| Condition loop | WHILE...ENDWHILE | Repeat while condition is true |
| Post-test loop | REPEAT...UNTIL | Repeat until condition is true |
| Terminator | Oval / Rounded rectangle | START and END of the algorithm |
Practice (10 minutes)
Q: What shape is used in a flowchart to represent a decision?
Answer: A diamond shape is used to represent a decision in a flowchart.
Plenary (5 minutes)
Explain Back
Your student teaches the key points back to you without looking. Fill any gaps immediately.
Lesson 3: Application: representing algorithms
Duration: 50 minutes
Starter Activity (5 minutes)
Quick Recall
Recall the key terms: Pseudo-code, Flowcharts, Decomposition. Define each in one sentence.
Main Content (35 minutes)
Parent/Teacher Guide: Let your student attempt each question alone first, then compare with the model answer. Award method marks for correct working even if the final answer is wrong.
Q1: What shape is used in a flowchart to represent a decision?
Answer: A diamond shape is used to represent a decision in a flowchart.
Q2: Write pseudo-code that asks the user for a number and outputs "Even" if it is divisible by 2, or "Odd" if it is not.
Answer: INPUT number IF number MOD 2 = 0 THEN OUTPUT "Even" ELSE OUTPUT "Odd" ENDIF
Q3: Explain the difference between decomposition and abstraction.
Answer: Decomposition breaks a complex problem into smaller sub-problems that can be solved independently. Abstraction removes unnecessary detail so you can focus on what is essential to solve the problem.
Q4: A program needs to calculate the area of a rectangle. Identify the inputs, processing and outputs.
Answer: Inputs: length and width of the rectangle. Processing: multiply length by width. Output: the area of the rectangle.
Q5: Decompose the problem of creating an online shopping system into at least four sub-problems.
Answer: Sub-problems: 1) Browse/search products, 2) Add items to basket, 3) Process payment, 4) Manage delivery details, 5) Handle user accounts.
Plenary (5 minutes)
Error Review
Review any questions answered incorrectly. Identify whether the error was knowledge, method, or reading the question.
Lesson 4: Exam Practice: representing algorithms
Duration: 50 minutes
Starter Activity (5 minutes)
Command Words
Review what these command words require: state (one point), describe (say what happens), explain (say why), compare (both sides), evaluate (judgement).
Main Content (35 minutes)
Exam-Style Question
Attempt a past-paper style question on representing algorithms from the exam board past paper finder (see Resources), then mark it against the scheme.
Exam Tips: Always use the correct pseudo-code keywords: IF, THEN, ELSE, ENDIF, WHILE, ENDWHILE, FOR, TO, NEXT | Flowchart decision boxes must have exactly two exits (Yes/No) | When asked to decompose, break the problem into at least 3-4 sub-problems | When asked about abstraction, explain WHAT detail is removed and WHY | Use the left-arrow symbol for assignment in pseudo-code, not = | Remember: decomposition splits up, abstraction strips down
Common Errors: ✗ Using = instead of ← for assignment in pseudo-code ✓ In pseudo-code, use the left-arrow ← for assignment; = is used for comparison in conditions. ✗ Thinking pseudo-code must follow exact Python/Java syntax ✓ Pseudo-code is language-independent structured English; it describes logic without strict syntax rules. ✗ Forgetting that flowchart decision boxes must have exactly two exits ✓ Every diamond (decision) must have exactly two paths: Yes and No. A decision with one exit is invalid. ✗ Confusing decomposition with abstraction ✓ Decomposition breaks a problem into smaller sub-problems; abstraction removes unnecessary detail to simplify.
Stretch & Challenge (Grade 8-9):
- Synoptic links: explain how representing algorithms connects to another Computer Science topic you have studied
- Real-world: research one real-world use or example of representing algorithms
- Critical: "What are the limitations of the models used in representing algorithms?"
Plenary (5 minutes)
Assessment Criteria
- Got it: Confident explanation + correct worked examples
- Getting there: Main points OK, needs support with detail
- Not yet: Confused on key concepts - re-run Lesson 2
Homework & Consolidation
- Consolidation: Re-answer any Lesson 3 practice questions answered incorrectly (20 mins)
- Retrieval: Write flashcards for the key terms: Pseudo-code, Flowcharts, Decomposition (10 mins)
- Exam practice: One past-paper question on representing algorithms from the board websites (15 mins)
- Extension: Explain representing algorithms to someone else in your own words (10 mins)