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IB Computer Science Paper 2: Thinking, Code and OOP
Computer Science: answer the question type first
Paper 2 covers Theme B: B1 computational thinking, B2 programming, B3 object-oriented programming. Each part has its own answer form – written steps in B1, runnable code in B2, attributes, methods and a reason for encapsulation in B3. The wrong form scores zero however good the content, so read the verb first: state, describe, construct, explain.
How is IB Computer Science Paper 2 assessed, and what does each part carry?
Paper 2 (Theme B): B1 computational thinking + B2 programming + B3 OOP; SL 50 marks (HL 8 (SL 35%／HL 40%); Paper 1 (Theme A + case study): A1-A4 concepts + case study; SL 50 marks (HL 80) (SL 35%／HL 40%); Internal assessment (computational solution): a computational solution to a self-chosen problem (SL 30%／HL 20%)
Assessment at a glance (2027)
| Component | Content | Weighting | Duration |
|---|---|---|---|
| Paper 2 (Theme B) | B1 computational thinking + B2 programming + B3 OOP; SL 50 marks (HL 80) | SL 35%／HL 40% | SL 1 h 15 min / HL 2 h |
| Paper 1 (Theme A + case study) | A1-A4 concepts + case study; SL 50 marks (HL 80) | SL 35%／HL 40% | SL 1 h 15 min / HL 2 h |
| Internal assessment (computational solution) | a computational solution to a self-chosen problem | SL 30%／HL 20% | 35 hours |
IB Computer Science Paper 2 drilling technique: do the B1 question that needs no code first (about 22 minutes), stating steps, inputs, outputs and edge cases in words; B2 wants runnable code (marks sit in variables, loops, selection and return), and if the question forbids built-ins, do not reach for sort(); B3 needs attributes, methods and a reason for encapsulation. Every programming question exists in Python and Java – answer in the language you were taught.
What each paper is actually testing
| Paper | Drill focus | How marks are lost |
|---|---|---|
| Paper 2 (Theme B) | B1 algorithmic thinking first, code and OOP after | The B1 algorithm is written as code when the question asks for written steps, so the wrong form scores nothing. |
| Paper 1 (Theme A + case study) | concepts + case study analysis | The B2 answer calls a built-in the question forbids, such as sort(), and the question scores zero. |
| Internal assessment (computational solution) | design, develop, evaluate | The B3 answer lists attributes but no methods and no reason for encapsulation, so the structure marks go. |
What is each IB Computer Science Paper 2 paper really testing, and what should you drill?
Paper 2 (Theme B): B1 algorithmic thinking first, code and OOP after; Paper 1 (Theme A + case study): concepts + case study analysis; Internal assessment (computational solution): design, develop, evaluate
Drill order: by topic, then by year, then the mark scheme
| Step | What you do | Why |
|---|---|---|
| 1. By topic | Work through each topic, starting with the paper that allows least help (no calculator / closed book) | Exposes what is genuinely not understood |
| 2. By year | Whole papers to time, one or two a week | Trains pace, stamina and question selection |
| 3. Mark scheme | Go through the marking scheme question by question and log the scoring steps you missed | Most lost marks are written wrong, not thought wrong |
Should drilling go by topic first or by year?
By topic first, then whole papers by year, then the mark scheme. The first third of the time goes topic by topic (8-10 years of the same topic back to back), the middle switches to timed whole papers, and the last fortnight only redoes the recurring errors from your log.
A 12-week drilling timetable
| Week | Phase | What to do |
|---|---|---|
| Weeks 1-3 | By topic: foundation | Topic by topic, starting with the easiest marks, building habits and recall |
| Weeks 4-6 | By topic: core | 8-10 years of the same topic back to back, errors classified by topic |
| Weeks 7-8 | By topic: advanced and electives | Elective and higher-order topics, now under time pressure |
| Weeks 9-10 | By year: timed papers | One full paper a week, timed, no reference materials |
| Week 11 | Mark scheme work | Question by question against the marking scheme; list the scoring steps you omitted |
| Week 12 | Plug holes and simulate | Only the recurring errors from your log, then one full exam simulation |
Subject-specific weighting for this timetable: Weeks 1-3: B1 computational thinking. Written input, steps, output and edge cases only, no code.
Weeks 4-6: B2 programming. One variable line per loop in trace questions, then hand-write sorting and searching without built-ins.
Weeks 7-9: B3 OOP and data structures. Attributes, methods and the reason for encapsulation, plus the cost of the chosen structure.
Weeks 10-12: whole papers to time, B1 first (about 22 minutes); redo only the questions answered in the wrong form.
Use it properly: this is not a checklist to finish. Every week must keep time for redoing errors, or from week 9 you will be repeating the same batch.
Pacing
| Paper | Time | Suggested split |
|---|---|---|
| Paper 2 (Theme B) | SL 1 h 15 min / HL 2 h | about 20 min B1, 20 min B2, 30 min B3 |
| Paper 1 (Theme A + case study) | SL 1 h 15 min / HL 2 h | about 55 min Section A, 20 min Section B |
| Internal assessment (computational solution) | 35 hours | run it alongside Papers 1 and 2, not at the end |
How should the time be split inside each IB Computer Science Paper 2 paper?
Paper 2 (Theme B): about 20 min B1, 20 min B2, 30 min B3; Paper 1 (Theme A + case study): about 55 min Section A, 20 min Section B; Internal assessment (computational solution): run it alongside Papers 1 and 2, not at the end
The drilling mistakes that cost the most marks
| Mistake | What it looks like | What actually happens | Instead |
|---|---|---|---|
| Trace answer only | No per-iteration values | Process marks are most of the total | One line of total per iteration |
| Using a forbidden built-in | Calling sort() | Zero for that question | Write the sort or search yourself |
| OOP with attributes only | No methods, no reason for privacy | Loses every encapsulation mark | Attributes, methods, reason for private |
| Code where prose is asked | B1 wants written steps | Wrong question type | State input, steps, output in words first |
The error log and the mark scheme
Three columns: the answer as written, the command word and the scheme key words (steps, construct, encapsulation, trace), and whether the loss was the form, the syntax or a missing reason. Form errors come first – they take the whole question.
How many years should you drill?
The current course first assesses the new Theme B structure in 2027, and older Paper 2 papers weight the parts differently, so do not drill them wholesale. Start from the official specimen and current papers to fix the three answer forms.
How many years of past papers is enough?
The current course first assesses the new Theme B structure in 2027, and older Paper 2 papers weight the parts differently, so do not drill them wholesale. Start from the official specimen and current papers to fix the three answer forms.
Frequently asked questions
Is this page a mock paper or a drilling guide?
This is the IB Computer Science Paper 2 drilling guide: assessment structure, drill order, a 12-week timetable, pacing, common mark losses and the error-log method. For questions with answers, use the IB Computer Science Paper 2 mock papers linked under Related.
By topic or by year first?
By topic. Eight to ten years of the same topic back to back is what exposes repeating errors; going straight to whole papers just repeats the same batch under time pressure.
How should the error log be written?
Do not copy out questions. Per error record four things: question reference, which step failed (concept, wording, calculation), what the mark scheme requires, and the correct action next time.
May I answer in the language I have learned?
Yes – questions come in both Python and Java. Use whichever you write fluently and do not switch under exam pressure; syntax slips drag the method marks with them.
How do I score on B1 without code?
Numbered steps: input, processing, output, edge cases. The marks are for a complete, executable procedure, not for code.
Official references
| Resource | What to use it for |
|---|---|
| IB Computer Science subject brief (first assessment 2027) | Confirm the Paper 1/2 times and weightings |
| IB Computer Science curriculum update (IBO) | Theme A/B scope and the removal of Paper 3 |
| https://www.tutorzone.com.hk/en-ib-computer-science-paper-1-mock-2027/ | IB Computer Science Paper 1 drilling mock |
Related: IB Computer Science drill guide (two-paper order, 75-minute pacing) · IB Computer Science Paper 1 drilling mock · practice area · IB Digital Society Paper 1 mock
Next step: find a tutor / register as a tutor
After drilling, the hard part is telling a conceptual error from a writing error. Tell us the year group, the school and your available times, and TutorZone will match you with a tutor who knows the HKEAA assessment requirements.
Demand for tutors in this subject is steady, and those who can explain the marking scheme and where marks are won are especially sought after. Register free; you pay only when a match succeeds.
