Criterion B: Planning
Criterion B shows how you broke the problem into manageable parts and how you planned to build them. The IB guide says the plan must be consistent with Criterion A, address the success criteria and give a proposed chronology for planning, designing, developing, testing and evaluating.
What you need to produce
- A decomposition of the problem into components and sub-tasks (a diagram plus short explanation)
- A chronological plan covering all five stages, with every task linked to success criteria (for example a Gantt chart or an Agile board)
Word budget
About 100 counted words. Most of the evidence is diagrams (decomposition and plan), which do not count; the words explain the decisions behind them. Put the detail (sub-tasks, SC codes, dates) inside the diagrams, where it is free. Words that label or identify a diagram (its caption, the labels in it) are not counted either; headings are, so keep them short. See how words are counted and allocated.
Subsections
| Subsection | Words (plan) | Suggested range | Main evidence |
|---|---|---|---|
| B1 Decomposition | 45 | 35–60 | explains the decomposition diagram |
| B2 Plan | 55 | 45–70 | explains the Gantt chart |
Each subsection below has the same seven parts: purpose, what to include, suggested length, a worked example, supporting evidence, lessons from the IB exemplars and a completion checklist. Labels show where each piece of guidance comes from:
Official level descriptors for Criterion B (best-fit marking)
| Marks | Level descriptor (IB Computer Science guide) |
|---|---|
| 0 | The response does not reach a standard described by the descriptors below. |
| 1–2 | constructs a partial decomposition of the problem scenario constructs a plan that addresses some of the success criteria of the solution |
| 3–4 | constructs a reasonable decomposition of the problem scenario constructs a plan that addresses the success criteria of the solution |
1 Purpose
Show that the problem from Criterion A has been broken down into essential components and sub-tasks that are small enough to design, build and test, and that support the plan.
2 What to include
- IB requirementBreak the problem scenario into smaller, more manageable sub-problems or components. The IB notes this “can be effectively constructed using diagrams”.
- IB requirementA reasonable decomposition (3–4 band) breaks the problem into the essential components that support the construction of a plan.
- IA GuideGo from major components to sub-tasks, and make them specific to your project: not “build the GUI”.
- IA GuideAdd supporting written text: diagrams alone are not enough.
- Teaching tipLabel each component with the success criteria it delivers. This makes the link to the plan and the evaluation obvious and shows nothing is missing.
- Teaching tipSay which component others depend on; that explains the order of your plan.
3 Suggested length
About 40–60 counted words (planning allocation 50) plus the decomposition diagram, which is not counted, and nor is its caption. The words explain the reasoning: which component is hardest, what depends on what.
4 Worked example
I decomposed PracticePal into six components, each labelled with the success criteria it delivers (Figure B1). Booking rules is the largest, because SC4–SC6 must pass together in one transaction; the waiting list and check-in depend on it, so it is built first.
Scroll sideways to see the whole diagram.
5 Supporting evidence (to be added to your appendix)
- A decomposition diagram: a top-down tree like Figure B1 or a mind map. See the decomposition example page.
- Related: B1.1.2 computational thinking concepts (decomposition).
- Do not confuse the decomposition (the problem, broken down) with the structure chart in C (the program's modules). They often look similar, but the structure chart shows calls and data passed between modules.
6 Lessons from the IB exemplars
From the IA Documentation Guide's analysis of real, examiner-graded IB Computer Science IAs.
- Diagrams with zero supporting text were capped at 2/4.For your IA: Write a short paragraph explaining the decomposition, even if the diagram is clear.
7 Completion checklist
Ticks are saved in this browser only, so you can use the list while you draft.
1 Purpose
Show a realistic order of work, written before you build, that covers every stage and every success criterion.
2 What to include
- IB requirementConstruct a plan that addresses the success criteria of the solution (3–4 band); “some of the success criteria” only reaches 1–2.
- IB requirementInclude a proposed chronology for planning, designing, developing, testing and evaluating. GANTT and AGILE charts are suggested formats.
- IB requirementYou may include relevant research, such as existing code libraries you plan to use.
- IA GuideCover all five stages: Plan, Design, Develop, Test, Evaluate. Do not skip Design or Evaluate.
- IA GuideLink every task to a success criterion number.
- IA GuideUse real dates and durations, and write the plan before you build: it is a plan, not a diary.
- IB FAQAgile planning is fine, and the plan may change while you develop the product. But planning is a design activity: write it before the product is built, and do not rewrite it afterwards to match what happened.
- Teaching tipShow dependencies (which task must finish first) and one or two milestones, such as the draft deadline your teacher gives you.
3 Suggested length
About 45–70 counted words (planning allocation 55) plus the plan itself. A Gantt chart drawn as a diagram is not counted, and nor is a plan written as a table with short entries (tasks, dates, SC codes). Any table cell written as a sentence of explanation does count, so use the words for the reasoning behind the order.
4 Worked example
The Gantt chart (Figure B2) covers all five stages over fourteen weeks, up to the draft deadline on 11 December. Each task lists its success criteria and the task it follows. The booking rules (V3) come early and get three weeks, because later features rely on them; unit tests run alongside development.
Scroll sideways to see the whole diagram.
5 Supporting evidence (to be added to your appendix)
- A Gantt chart (Figure B2) or an Agile board with sprints, as long as each item is linked to success criteria and dated. See the Gantt chart example page.
- Any research you did before building (for example, which scheduling library to use) can be one line in the plan.
6 Lessons from the IB exemplars
From the IA Documentation Guide's analysis of real, examiner-graded IB Computer Science IAs.
- Full marks (4/4) only went to plans naming all 5 stages AND linking tasks to success criteria.For your IA: Check both: five stage headings, and an SC column with no blanks.
- A detailed, great-looking Gantt chart with no SC links still scored low.For your IA: Appearance earns nothing on its own; the links to success criteria do.
7 Completion checklist
Ticks are saved in this browser only, so you can use the list while you draft.
Full worked examples, each with notation, common mistakes and a checklist.
Criterion B worked examples: word total
| Subsection | Planning allocation | Worked example (counted words) |
|---|---|---|
| B1 Decomposition | 45 | 43 |
| B2 Plan | 55 | 52 |
| Total | 100 | 95 |
The fictional PracticePal documentation uses 95 of the 100 counted words planned for Criterion B. Across all five criteria it stays within 2,000; see the budget table.