IB DP Computer Science: Paper-by-Paper Exam Preparation

The assessment revision notes set out what Paper 1 and Paper 2 weigh and test. These notes turn that into an exam-day plan – how to use the pre-seen case study, what to practise for Paper 2’s algorithmic questions, and a worked scenario – alongside the full syllabus guide and subject overview already on the site.

Paper 1: use the pre-seen case study as active research material

Paper 1’s case study is released well before the exam, so questions drawing on it are, in effect, partially predictable – research and familiarity built beforehand translate directly into faster, more confident answers. Treat the case study as material to actively analyse and annotate over the weeks before the exam, not background reading to skim once: identify likely question angles (how would this organisation’s system need to scale, what security concerns would it face, what trade-offs would its design involve) and prepare short notes on each, since case-study questions carry a meaningful share of Paper 1’s marks and reward genuine familiarity over surface recognition.

Paper 1’s extended-response questions on core concepts otherwise use command terms consistent with the DP sciences group – define, identify, outline at the lower tier; explain, describe, compare in the middle; evaluate, discuss, justify at the top, often applied directly to the case study.

Paper 2: algorithmic thinking, answered in Java or Python

Paper 2 is set on Theme B and focuses on solving problems through algorithmic thinking. For this course (first assessment 2027), candidates answer Paper 2 in either Java or Python, and all students are assessed on questions that require knowledge of programming. The outgoing course assessed algorithms in pseudocode, so revision material that tells you to prepare “in pseudocode, not a language” is describing that course, not this paper. The common mistake now runs the other way: revising only the logic of algorithms without writing, running and debugging real code in the language your course uses.

Exam-preparation priority: practise tracing code by hand – writing out variable values line by line as it executes – and practise writing short programs in your course language from a described problem. Tracing is a mechanical skill that improves quickly with deliberate practice, and it underpins both questions that ask you to predict what code does and questions that ask you to write code, where you should check how your own code behaves before committing it to the answer.

Worked practice scenario: tracing a loop

A Paper 2-style question gives the following code and asks you to trace it, stating the value of total after the loop finishes, for the input list [4, 7, 2, 9]. It is shown in Python; the Java version has the same logic.

total = 0
for value in values:
    if value > 5:
        total = total + value
print(total)

Trace table:
  value = 4   ->  4 > 5 is FALSE   ->  total stays 0
  value = 7   ->  7 > 5 is TRUE    ->  total = 0 + 7 = 7
  value = 2   ->  2 > 5 is FALSE   ->  total stays 7
  value = 9   ->  9 > 5 is TRUE    ->  total = 7 + 9 = 16

Output: total = 16

A trace-table answer like this – one row per iteration, showing the condition checked and the variable’s value after each step – is exactly the structured working “trace” questions reward. Writing out each iteration explicitly, rather than trying to compute the final answer mentally, both reduces careless errors and shows the working examiners need to award method marks even if the final value is wrong.

Before/during exam checklist

• Before the exam: research and annotate the Paper 1 pre-seen case study across several weeks, not just once; practise hand-tracing loops and conditionals until a trace table is automatic; practise writing, running and debugging short programs in Java or Python (whichever your course uses) from a described problem.
• During Paper 1: draw explicitly on prior research into the case study where a question references it, rather than answering as if it were entirely unfamiliar.
• During Paper 2: always build a trace table for “trace” questions rather than computing the answer mentally; for questions that ask you to write code, briefly trace your own code against a simple example before finalising it, to catch logic errors before submitting.
• On every paper: match your answer’s command term to the question – a “define” or “identify” question needs a short, precise answer; “evaluate,” “discuss” and “justify” need a reasoned judgement.

Self-test

1. Why is Paper 1’s case study, in effect, partially predictable exam content?
2. In what form do candidates answer Paper 2 on this course, and what does that mean for revision?
3. Using the worked scenario’s code and the input list [4, 7, 2, 9], what is the value of total after the loop finishes?
4. Why does building a trace table help even when the final traced value is wrong?
5. What should you do before finalising code you have written in answer to a question?

Answers: 1. Because it is released well before the exam, so research and familiarity built beforehand translate directly into faster, more confident answers on questions drawing on it. 2. In Java or Python, and every student faces questions requiring programming knowledge — so revision must include writing and debugging real code in the course language, not only reasoning about algorithms in the abstract. 3. 16 (0 + 7 + 9, since only values greater than 5 – namely 7 and 9 – are added to the running total). 4. Because a clear, step-by-step trace table shows the working and method used, which lets examiners award method marks even if a small error means the final traced value is incorrect. 5. Briefly trace the written code against a simple example to check its logic works as intended, catching errors before committing to the final answer.

Official syllabus

International Baccalaureate Organization, Diploma Programme Subject Brief – Sciences: Computer Science, first assessment 2027, published 2024 – the same source cited by the assessment revision notes and full syllabus guide. The worked scenario above is an original example written for this resource, not a reproduction of any official past or sample paper question.