Maths IA criteria · 4 marks
Criterion B: Mathematical communication
Criterion B is about writing mathematics properly: the right notation, terminology and representations, used consistently throughout. It is worth 4 marks, and small, fixable slips cost students more marks here than anywhere else.
Next step: check your plan or draft free with the IA self-check — guided questions give a rough band for each criterion, no upload. For feedback on your own draft, the IA package (€39 once) gives you 5 AI feedback credits and every annotated exemplar in full.
What Criterion B assesses
Whether the mathematical language — notation, symbols, terminology — is appropriate and used consistently, whether key terms and variables are defined, and whether the representations you choose (graphs, tables, diagrams, equations) are relevant and clear.
This is our summary, not the IB's wording. The descriptors themselves, with a checklist and a self-grade sheet, are on the IA criteria page. For a rough band for your own draft, answer the guided questions in the free IA self-check.
What the mark bands look like in practice
| Band | What the examiner typically sees |
|---|---|
| Low (1) | Some relevant mathematical language, but notation is often wrong or informal (calculator notation, undefined variables). |
| Middle (2) | Relevant notation and some suitable representations, but used inconsistently — for example correct symbols in one section and calculator notation in the next, or graphs without labelled axes. |
| Good (3) | Mostly appropriate and consistent notation, terminology and representations, with occasional slips. |
| Top (4) | Appropriate and consistent throughout: every variable defined, every graph labelled with units and scale, rounding justified, and representations chosen because they help. |
Our summary in plain English, not IB wording — see the official IB guide via your teacher.
Checklist for Criterion B
- Every variable defined when it first appears, with units and domain (e.g., “let t be the time in minutes, t ≥ 0”).
- Key terms defined where they are first used — not in a glossary at the start.
- No calculator or computer notation: write x², not x^2; e^(0.5t) as a proper exponent; √ not sqrt; × not *; E for standard form never.
- ≈ for every rounded value, and a sentence explaining your rounding (e.g., to 3 significant figures because the data were measured to 3 s.f.).
- Graphs with titles, labelled axes, units and scales; an axis break shown if an axis does not start at zero.
- Tables with headings and units in the column titles.
- Variables in italics, consistently (an equation editor does this for you).
- Equations typed in an equation editor, in the same font throughout.
- The word “substitute”, not “plug in”; mathematical vocabulary used accurately (gradient, asymptote, residual…).
- Only statistics you use: do not calculate a standard deviation you never interpret.
Examiner tips
Define, then use.
An examiner should never meet a symbol before you have said what it means. A quick way to check: search your document for each letter you use as a variable.
Choose representations that do work.
A scatter graph before you model, a residual plot after, a table of parameters when you compare models. A pie chart of your data rarely helps anyone.
Justify accuracy.
Say why your sample size and your level of rounding are appropriate. “Temperatures were recorded to 0.1 °C, so results are given to 1 decimal place” is exactly what examiners look for.
Weak vs strong: an example
Loses marks
“I plugged the numbers into the equation y=45e^-0.03x+20 and got 38.6421.”
Earns marks
“Substituting t = 20 into T(t) = 45e^(−0.03t) + 20, where T is the temperature in °C after t minutes, gives T(20) ≈ 38.6 °C (to 1 d.p., the precision of the thermometer).”
Common Criterion B mistakes
- Graphs pasted from software with default labels such as “Series 1” and no units.
- Writing 2.5E-3 or y=3x^2+2 in the text.
- Using = for rounded values.
- Changing the name of a variable half-way through.
- Defining all variables in a list at the start instead of when they appear.
What the IB subject reports say about Criterion B
- Computer and calculator notation (*, ^, E, equations typed as plain text) and missing ≈ signs are still the most common losses.
- Inconsistent variables (capital and lower-case letters for the same quantity, missing italics or subscripts) and variables never defined.
- GDC screenshots and step-by-step calculator or software instructions are not mathematical communication; use an equation editor and your own graphs.
- Graphs and tables dropped in with no sentence before or after them, graphs too small or unlabelled, and regression lines added to scatter plots by default.
- Choose a degree of accuracy that suits the context and keep it consistent, rather than applying the exam's 3 s.f. rule blindly.
Our own summary of the moderators' comments in the IB's Mathematics subject reports (AA and AI, SL and HL, May 2024 to November 2025), which the IB releases to schools. Not the IB's wording, and not an IB publication.
Frequently asked questions
Can I use screenshots from Desmos or GeoGebra?
Yes, if they are clear and fully labelled. Add a title, axis labels with units, and a figure number, and refer to the figure in your text. Many students redraw key graphs so the labels are consistent.
Do I need to type equations in an equation editor?
It is strongly recommended. It makes notation correct and consistent (italic variables, proper exponents and fractions), which is exactly what Criterion B rewards.
How should I round numbers in my IA?
Round to a precision that matches your data, say what it is, and use ≈ whenever a value is rounded. Keep full accuracy in intermediate calculations and round only the values you report.
Communicating a model: notation, variables, graphs
Define every variable with units and domain, write the fitted model in proper notation (≈ for rounded values, no calculator notation) and label every graph. Each worked model marks the steps where this matters with a Criterion B tip, and the common mistakes list what loses these marks.
Related: all five criteria with a self-grade sheet · annotated exemplars marked on every criterion · have Pete review your draft one-to-one · IA structure and format
Types of IA where notation needs particular care: numerical methods & error analysis · matrices, transformations & Markov chains · cryptography & number theory.
Free: the Criterion B checks, and the other four, in one PDF
The checklist Pete uses with his own students: every check for Criteria A–E (including the Criterion B list above) in a 4-page PDF, the mistakes that cost the most marks, and a self-assessment grid. We'll email it to you, and for three weeks your weekly email carries one IA tip, timed to your deadline if you give it. Free — no account, no payment.
While you wait for the email: see Criterion B at the top band in a free annotated excerpt →