MYP Maths Criterion A: Knowing & Understanding — Complete FAQ

According to the MYP: Mathematics guide (for use from September 2025), Criterion A is assessed against four descriptors at increasing difficulty:

1. Select appropriate mathematics when solving simple problems.
2. Apply the selected mathematics successfully.
3. Solve correctly in a variety of contexts.
4. Justify the degree of accuracy and describe results using appropriate terminology.

Quick tip: examiners give 7-8 to students whose working shows why a method was chosen, not just that it produced the right answer.

Think of it as the 'can you actually do the maths' criterion. Criterion B (Investigating Patterns) wants generalisation; Criterion C (Communicating) wants a coherent, well-labelled solution; Criterion D (Applying to Real-Life) wants context. Criterion A sits underneath all of them — if the maths itself is wrong, marks in the other criteria often collapse too.

MYP Criterion A mark bands

Most students plateau at 5-6 because they solve correctly but never explain why that method or degree of accuracy was appropriate.

Three habits that push students into band 4 in my classroom every year:

1. Round with reason. Don't just write '3.2 cm' — add 'rounded to 1 d.p. as the ruler measures to the nearest mm.'
2. Name the method. 'Using the quadratic formula because the expression doesn't factorise' beats a silent calculation.
3. Check the domain. State when a negative solution is rejected (e.g. length can't be negative) — that single sentence often separates 6 from 7.

Common mistake: leaving an answer as an unrounded decimal (e.g. 14.28571...) in a real-world context like money or people, with no comment. Correctly rounding to 2 d.p. for currency, or up to the nearest whole person, and stating why, is exactly the kind of justification that unlocks 7-8.

Question: A right-angled triangle has legs 5 cm and 12 cm. Find the hypotenuse.

Band 2 response: $5^2+12^2=169$, $\sqrt{169}=13$. Answer: 13.

Band 4 response: Using Pythagoras' theorem since the triangle is right-angled: $5^2+12^2=25+144=169$. $c=\sqrt{169}=13\text{ cm}$. As the original measurements are given as whole centimetres, 13 cm is already an appropriate degree of accuracy — no rounding needed.

Same maths, same final number — but only the second response names the theorem, shows reasoning for the method, and justifies the accuracy. That's the gap between 3-4 and 7-8.

Criterion A vs Criterion B

Because the MYP gives schools flexibility in how they design assessment tasks (per the MYP: From Principles into Practice guide), the exact format varies. What doesn't vary is the descriptor language — whatever the task looks like, it's still marked against select, apply, solve and justify.

The IB requires schools to assess every criterion at least once across the two years of MYP 4-5, but most schools do considerably more than the minimum to give students multiple chances to show improvement before the final grade is set.

How the four criteria combine

A weak Criterion A score can still be offset by strong B, C and D scores — but since A underpins the actual maths used elsewhere, it's rare to see a low A alongside high scores everywhere else.

Quick tip: don't just redo questions you already know how to solve. Pick problems set in unfamiliar contexts (a different unit, an odd shape, a non-round number) since that's precisely where band 3-4 descriptors are tested — 'a variety of contexts', including ones you haven't seen before.