Exploring Linear Search

Overview

This lesson introduces Year 7 students to the concept of linear search, a fundamental searching algorithm in computing. It aligns with the National Curriculum for England’s Computing programmes of study, specifically the understanding of algorithms, programming, and computational thinking. The lesson uses the I DO, WE DO, YOU DO teaching model to scaffold learning with built-in differentiation to support all learners.

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National Curriculum Links

Key Stage 3 – Computing

• Pupils should be taught to:
  • Understand how algorithms work and apply them on real-world problems.
  • Design, write and debug programs that use sequences and repetition, including input and output.
  • Use logical reasoning to explain how simple algorithms work, including those that search and sort data.

This lesson specifically addresses:

• Program design and computational thinking (NC ref: KS3 Computing - Design, use and evaluate computational abstractions that model the state and behaviour of real-world problems and physical systems.)
• Algorithms and problem solving (NC ref: KS3 Computing - Use logical reasoning to detect and correct errors in algorithms and programs.)

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Learning Objectives

By the end of this 60-minute lesson, students will be able to:

1. Explain what a linear search is and when it is used.
2. Demonstrate how a linear search algorithm works on a list of data.
3. Design and write a simple linear search program/pseudocode using appropriate computational thinking symbols.
4. Evaluate the efficiency of linear search compared to other searching methods.

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Resources Needed

• Whiteboard and markers
• Student computers/tablets with a simple coding environment (e.g., Scratch, Python IDE, or online block-based coding platform)
• Printed worksheets with data lists and linear search pseudocode templates
• Projector/display for visual demonstration
• Flashcards or cards with numbers/words for a physical linear search activity
• Differentiated worksheets (basic, intermediate, and challenge levels)
• Timer/stopwatch for pacing activities

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Lesson Structure

Introduction (10 minutes) - I DO

Goal: Teacher models and explains linear search concept clearly with real-life analogy and demonstration.

1. Hook (5 minutes):

   • Use a relatable scenario: “Imagine you lost your favourite book in a messy pile of books. How would you find it?”
   • Discuss everyday searching strategies.
   • Introduce linear search as the step-by-step approach to find an item in a list.

2. Teacher Explanation (5 minutes):

   • Present a simple example on the whiteboard: searching for number 7 in a list [3, 5, 7, 9, 11].
   • Step through the search sequentially, verbalising the process and decision at each step.
   • Show a flowchart or pseudocode of linear search.
   • Highlight its efficiency (O(n)) and when it is practical to use.

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Guided Practice (20 minutes) - WE DO

Goal: Students practice linear search step-by-step in collaboration with the teacher.

1. Physical Activity (10 minutes):

   • Shuffle pre-prepared cards with numbers or words.
   • Students work in pairs: one student picks a number to find, the other physically performs the linear search by moving through the cards sequentially, verbally describing each step aloud.
   • Swap roles after each turn.
   • Teacher circulates to support and ask probing questions.

2. Coding Activity (10 minutes):

   • On devices, students follow guided instructions to write or modify a simple program/pseudocode that implements linear search.
   • Teacher projects code and works through it together with the class, encouraging students to predict outputs and debug as needed.
   • Use block-based or text-based coding depending on class confidence level.

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Independent Practice (20 minutes) - YOU DO

Goal: Students independently apply their learning to complete tasks with differentiated support.

1. Task:

   • Students complete a worksheet containing:
     • Tracing a given linear search algorithm on a new list to identify the steps taken.
     • Writing pseudocode for linear search with minimal prompts.
     • A challenge question comparing linear search to binary search (discussion or short written explanation).

2. Differentiation:

   • Support for SEND learners: simpler tasks with step-by-step hints and visual aids.
   • Extension for more able learners: design an algorithm to find multiple occurrences of a value or estimate the number of steps needed for large lists.

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Plenary and Assessment (10 minutes)

1. Class Discussion:

   • Recap key points of linear search.
   • Ask students to explain how linear search works in their own words.
   • Discuss the efficiency and disadvantages briefly.

2. Quick Quiz / Exit Ticket:

   • True/False or multiple-choice quiz questions on the key concepts.
   • Example: “Linear search checks every item until it finds a match - True or False?”
   • “Which scenario is linear search most suitable for?”

3. Formative Assessment:

   • Review worksheet answers to identify misconceptions.
   • Observe pair activity to gauge student understanding and engagement.

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Adaptive Teaching Strategies for Differentiation

• Visual learners: Use flowcharts, diagrams, and physical card activities.
• Auditory learners: Encourage verbal explanation and group discussions.
• Kinesthetic learners: Use physically moving cards to simulate searching.
• Cognitive scaffolding: Chunk tasks sequentially during guided practice, provide examples and sentence starters for pseudocode.
• Technology adaptation: Use block-code for lower ability students and text-based for advanced.
• Peer support: Pair stronger students with those needing additional guidance.
• Time management: Allow flexible time for ‘YOU DO’ based on student progress.

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Additional Notes for Teachers

• Encourage metacognition by prompting students to think about why linear search might not be efficient for very large datasets.
• Link this lesson to previous topics in computational thinking and prepare them for upcoming lessons on binary search and sorting algorithms.
• Highlight real-world applications such as searching for files on computers or finding entries in phone contacts.
• For remote or hybrid teaching, digital equivalents of card activities can be used, such as drag-and-drop online games or apps modelling linear search.

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By following this structured lesson plan, teachers will deliver a research-backed, engaging, inclusive and curriculum-aligned introduction to linear search that addresses diverse student needs and builds a strong foundation for future algorithm studies.