LNF Cymru Literacy and numeracy for Wales

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GCSE Computer Science

Numeracy is heavy and specific: learners convert between denary, binary and hexadecimal, add in binary, work with base 2 storage units, calculate image, sound and compressed file sizes and routing costs, and reason with truth tables and DIV and MOD. Literacy centres on close reading of the Unit 2 scenario and requirements, precise technical vocabulary, short and extended judgement answers in Unit 1, and code annotation and test commentaries. The single biggest thing Key Stage 3 should build is fluent place value in base 2 and base 16, so that storage and file size calculations become routine.

First taught
September 2025
Amount of literacy work
Medium
Amount of numeracy work
High
Specification
Open the WJEC specification (PDF)
How this GCSE is assessed
  • Unit 1: Understanding Computer Science: Digital examination 1 hour 30 minutes, 50%, 80 marks
  • Unit 2: Computer Programming: On-screen examination based on a pre-released brief, 2 hours, 50%, 80 marks, set and marked by WJEC

Skills that use Measurement

  1. Data storage units and capacity

    Assessed: In the exam

    Learners must know the base 2 storage units from bit and nibble to petabyte, where each step is 1,024 not 1,000, and calculate the capacity needed to store data.

    Numeracy: Measurement, Calculation, The number system, Relationships within the number system, Communicating with symbols, Fluency, Conceptual understanding

    Getting pupils ready

    Year 7
    Pupils order bit, nibble, byte, kilobyte, megabyte and gigabyte on a class washing line and work out how many bits are in one kilobyte.
    Year 8
    Pupils work out how many 3 MB photos fit on a 16 GB memory stick, first estimating with 1,000 and then calculating with 1,024, and explain the difference.
    Year 9
    Pupils total the file sizes in a sample project folder, convert the total into the most sensible unit and judge whether it fits their school network storage allowance.
    Show the specification wording and the LNF statements

    Where it is in the specification: Unit 1, Section 1.2.1, pages 13 to 14

    “the relationship between data storage units using the base 2 prefixes”
    Progression step 3

    • I can convert metric units of length to smaller units, e.g. cm to mm, m to cm, km to m.

    • I can multiply numbers and decimals by a multiple of 10, e.g. 15 x 30, 1.4cm x 20.

    • I can read and write numbers to 1 million and numbers to 3 decimal places.

    Progression step 4

    • I can use the common units of measure, convert between related units of the metric system and carry out calculations.

    • I can use powers and understand the importance of powers of 10.

    • I can read and write numbers of any size.

    Progression step 5

    • I can use appropriate notation, symbols and units of measurement, including compound measures.

    • I can use firmly established, memorable and usable facts and techniques in order to apply the most efficient methods.

    • I can interpret answers within the context of the problem and consider whether answers, including calculator, analogue and digital displays, are sensible.

  2. Calculating file sizes for images and sound

    Assessed: In the exam

    Learners calculate the storage needed for graphics from dimensions and colour depth, and for sound from sampling rate, bit depth and length, then convert the result into suitable units.

    Numeracy: Shape and space, Calculation, Strategic competence, Measurement, Communicating with symbols

    Getting pupils ready

    Year 7
    Pupils draw an 8 by 8 pixel icon on squared paper using four colours, find the number of pixels as an area and work out that each pixel needs 2 bits.
    Year 8
    Pupils use width times height times colour depth to calculate the file size of their pixel art in bits and bytes, then predict what doubling the colour depth does.
    Year 9
    Pupils record a 10 second sound clip in Audacity, calculate its size from sample rate, bit depth and length, and compare their answer with the saved file size.
    Show the specification wording and the LNF statements

    Where it is in the specification: Unit 1, Section 1.2.1, page 13

    “how to calculate the storage requirements for graphics using different dimensions, bit depths and colour depths.”
    Progression step 3

    • I can find areas by counting squares, progressing to calculating the area of squares and rectangles using formulae.

    • I can multiply 2- and 3-digit numbers by a 2-digit number.

    • I can prioritise and organise the relevant steps needed to complete the task or reach a solution.

    Progression step 4

    • I can demonstrate an understanding of the relationship between a formula representing a measurement and the units used.

    • I can use the order of operations including brackets and powers.

    • I can prioritise and organise the relevant steps needed to complete the task or reach a solution.

    Progression step 5

    • I can recognise, model and apply the underlying mathematical structures and ideas within problems, in order to formulate and solve them.

    • I can refine methods of recording calculations.

    • I can understand and use a variety of compound measures.

Good to know

Links with other GCSEs

Place value, powers, ratio and percentage reduction are taught in Mathematics, so agreeing shared language (for example 'column value' and 'simplest form') with the Mathematics department in Years 7 to 9 will help pupils transfer these skills to binary and file size work.

Source: WJEC GCSE Computer Science specification, teaching from 2025, for award from 2027, Version 3, September 2025.