WJEC A-Level Computer Science Unit 2 Practical Programming to Solve Problems: how the on-screen examination works and how to prepare
A WJEC A-Level Computer Science guide to Unit 2 Practical Programming to Solve Problems, the AS on-screen examination. Explains how the unit is assessed, the design-implement-test method for solving set problems, choosing data structures, validating input, and systematic testing with normal, boundary and erroneous data.
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What Unit 2 actually demands
Unit 2 Practical Programming to Solve Problems is the AS practical unit, assessed by an on-screen examination. Rather than answering a written paper, you sit at a computer and produce working programs that solve problems WJEC sets. The unit does not add new theory: it assesses your ability to apply the programming principles of Unit 1 at a keyboard, under time pressure, with the program actually running.
Because it is a skills unit, this guide is shorter than the content-heavy units and focuses on method and preparation. There is one matching dot-point page; this overview frames the approach.
How the unit is assessed
Unit 2 is an on-screen practical examination contributing 37.5 per cent of the AS and 15 per cent of the full A level. You design, write and test solutions during the exam itself, so fluency matters: you must be able to write structured code quickly and correctly without referring to notes for basic syntax.
The design-implement-test method
A reliable approach has four stages.
- Understand the problem. Identify the inputs, the required outputs, and the processing that links them. Misreading the problem is the most expensive early mistake.
- Design. Plan in pseudocode or a structure diagram, decomposing the solution into procedures and functions before writing any code.
- Implement. Write structured, readable code using sequence, selection and iteration, with meaningful identifiers and appropriate data structures.
- Test. Run the program against a planned set of test data and correct any faults found.
Choosing data structures and validating input
Choose the structure that fits the data: an array or list for many items of one type, a record for grouped fields of different types. Validate input with range, type, presence, format and length checks so the program does not crash on bad data. Robust programs that handle unexpected input score better than fragile ones that only work on ideal data.
Testing systematically
Test with three categories of data: normal (typical valid input), boundary (values at the edges of the allowed range, where off-by-one errors lurk), and erroneous (clearly invalid input that should be rejected). Record the expected and actual result for each test, and fix any mismatch. A documented test plan is both good practice and the way to demonstrate a working, reliable solution.
How to prepare
The only reliable preparation for a practical exam is to program. Practise the full method on past sample tasks, rehearse common patterns (reading into arrays, traversing with loops, searching, sorting, using records), and write test plans until they are automatic. Debug your own errors rather than asking for fixes, because finding and correcting faults under time pressure is exactly what the exam tests.
The matching dot point
The unit has one dot-point page setting out the practical approach in more detail, with worked exam-style questions and cross-links to the Unit 1 programming principles it applies. Browse it from this overview and the subject hub.
For the official specification
WJEC publishes the full specification, sample assessment materials and past papers at wjec.co.uk. Always prepare from the current specification and WJEC's own materials, because the on-screen exam arrangements and permitted languages are board-specific.