Introduction to Algorithms

Algorithms feel abstract until students experience their power through movement and collaboration. Active tasks like directing peers or testing instructions by hand make the core traits of finiteness, definiteness, and feasibility tangible, turning definitions into lived understanding rather than abstract notes.

• Year 10
• Computing
• 4 activities
• 25 min–40 min

Learning Objectives

1. Identify the four key characteristics of a well-defined algorithm: finiteness, definiteness, feasibility, and defined inputs/outputs.
2. Compare and contrast the precision required for a computational algorithm versus everyday instructions, such as a recipe.
3. Analyze the role of algorithms in the functionality of specific technologies, including search engines and GPS navigation systems.
4. Design a simple algorithm to solve a given problem, ensuring all characteristics of a well-defined algorithm are met.

Think-Pair-Share

⏱ 30 min·Pairs

Pairs: Blind Drawing Algorithm

One student writes an algorithm with precise steps to draw a simple shape, like a house. Their partner follows instructions exactly without seeing the original, using paper and pencil. Pairs switch roles, then discuss ambiguities and refine the algorithm.

Prepare & details

Explain the key characteristics of a well-defined algorithm.

Facilitation Tip: For the Blind Drawing Algorithm, pair students back-to-back so one describes a simple image step-by-step while the other draws without seeing it, making ambiguity visible in real time.

Setup: Standard classroom seating; students turn to a neighbor

Materials: Discussion prompt (projected or printed), Optional: recording sheet for pairs

• Understand
• Apply
• Analyze
• Self-Awareness
• Relationship Skills

Think-Pair-Share

⏱ 40 min·Small Groups

Small Groups: Card Sorting Challenge

Groups receive shuffled cards with numbers or shapes and create a sorting algorithm in plain English. They test it by having another group execute it. Groups revise based on errors observed during execution.

Prepare & details

Compare algorithms to simple instructions, highlighting the differences.

Facilitation Tip: In the Card Sorting Challenge, give groups shuffled decks of numbered cards and ask them to sort by value without speaking, forcing them to refine instructions through trial and error.

Setup: Standard classroom seating; students turn to a neighbor

Materials: Discussion prompt (projected or printed), Optional: recording sheet for pairs

• Understand
• Apply
• Analyze
• Self-Awareness
• Relationship Skills

Think-Pair-Share

⏱ 25 min·Whole Class

Whole Class: Human Algorithm Line-Up

Students represent numbers and follow a teacher-led bubble sort algorithm to arrange themselves in order. The class observes swaps and iterations. Debrief on how physical movement highlights finiteness and definiteness.

Prepare & details

Justify the importance of algorithms in everyday technology.

Facilitation Tip: For the Human Algorithm Line-Up, have students physically move into order based on a set of written rules you provide, then discuss where breakdowns happened due to unclear criteria.

Setup: Standard classroom seating; students turn to a neighbor

Materials: Discussion prompt (projected or printed), Optional: recording sheet for pairs

• Understand
• Apply
• Analyze
• Self-Awareness
• Relationship Skills

Think-Pair-Share

⏱ 35 min·Individual

Individual: Everyday Task Flowchart

Students select a routine task, like making tea, and convert vague instructions into a flowchart algorithm. They self-test by following their own steps precisely, noting inputs, outputs, and potential improvements.

Prepare & details

Explain the key characteristics of a well-defined algorithm.

Facilitation Tip: Ask each student to draw a flowchart for an everyday task like brushing teeth, ensuring they use clear start/end points and unambiguous decision diamonds.

Setup: Standard classroom seating; students turn to a neighbor

Materials: Discussion prompt (projected or printed), Optional: recording sheet for pairs

• Understand
• Apply
• Analyze
• Self-Awareness
• Relationship Skills

Teaching This Topic

Start with human-scale tasks so students feel the frustration of vague instructions firsthand. Research shows this builds empathy and retention before introducing code or pseudocode. Use guided questioning (e.g. “Where did the instructions fail?”) to steer discussions toward algorithmic traits. Avoid rushing to definitions—instead, let students articulate characteristics from their experiences.

What to Expect

By the end of these activities, students will confidently distinguish clear instructions from vague ones, spot missing steps, and justify why precision matters. Their written and spoken explanations will show they can apply characteristics of good algorithms to both computational and everyday tasks.

Watch Out for These Misconceptions

Common Misconception

During Blind Drawing Algorithm, some students may think any description counts as an algorithm.

What to Teach Instead

Pause mid-activity and ask each drawer to point to the step where confusion happened, then have partners revise that step to make it definite before continuing.

Common Misconception

During Card Sorting Challenge, students might believe any method that sorts the cards is an algorithm.

What to Teach Instead

Ask groups to swap their final sorting steps with another group and have them test the borrowed instructions, forcing them to confront vagueness or missing steps directly.

Common Misconception

During Human Algorithm Line-Up, students may assume that if everyone follows instructions correctly, the outcome is always correct.

What to Teach Instead

Intentionally give an ambiguous rule (e.g. ‘stand beside someone taller’) and pause to ask why the line didn’t form as expected, linking failure to design flaws.

Assessment Ideas

Exit Ticket

After Everyday Task Flowchart, collect student flowcharts and ask them to circle one ambiguous step and rewrite it to be definite, submitting both versions for review.

Quick Check

During Card Sorting Challenge, circulate and ask each group to explain which of their sorting steps best demonstrates definiteness, then listen for references to clear, unambiguous actions.

Discussion Prompt

After Human Algorithm Line-Up, pose the prompt: ‘If the rules were feasible but took 20 minutes to execute, would you still call it a good algorithm?’ and facilitate a class vote with justification.

Extensions & Scaffolding

• Challenge pairs in Blind Drawing to describe a complex shape like a star with ten precise steps.
• Scaffolding for Card Sorting: provide pre-written starter steps on cards students must arrange before adding their own.
• Deeper exploration: ask students to redesign a flawed algorithm from Human Algorithm Line-Up to meet all four characteristics, then present their improved version.

Key Vocabulary

Algorithm	A set of step-by-step instructions designed to perform a specific task or solve a particular problem.
Finiteness	The characteristic of an algorithm that guarantees it will terminate after a finite number of steps.
Definiteness	The characteristic of an algorithm where each step is precisely and unambiguously defined, leaving no room for interpretation.
Feasibility	The characteristic of an algorithm that ensures all operations can be carried out with the available resources and within a reasonable time.
Input/Output	The data provided to an algorithm (input) and the result produced by the algorithm (output).