One Sibling Is Brilliant at Maths, the Other Struggles. How Families Navigate the Gap.

The difference in mathematical ability between siblings is one of the most common sources of family tension I encounter, and also one of the most underestimated. Parents often tell me they "try not to compare" and genuinely mean it — and then describe to me household arrangements that are structured entirely around the comparison they're trying not to make.

Let me describe the terrain as I see it from the classroom and the parent evening.

There is a reasonably strong genetic component to mathematical aptitude. This is established in the twin studies literature and shouldn't really be controversial, though it can feel uncomfortable to say because we've inherited a folk theory of achievement that attributes everything to effort and nothing to capacity. The practical implication is this: two children from the same parents, raised in the same environment, can have genuinely different mathematical ability. Not because one worked harder, not because one was taught better, but because they are different people.

This does not mean the less mathematically able child cannot improve or succeed. It means that a family hoping both children will reach the same mathematical attainment through the same amount of effort is holding an expectation that may simply be empirically incorrect.

When a family has one strong maths student and one weak one, several things happen that I observe across multiple families with remarkable consistency. First, the strong student becomes, implicitly, the model. Their results set the family's expectation of what is achievable. The weaker student is then measured against this implicit standard rather than against their own progress. A child who has made genuine improvement from 55% to 68% in a term feels, in this household, like they've still failed — because the sibling is getting 90%.

Second, and this is more delicate, the strong student sometimes develops a particular dynamic with the weaker one that is not good for either of them. I have seen brilliant maths students become contemptuous of their siblings' difficulty in ways that the parents enable by not naming it. "She's just better at maths" said casually in front of both children is a statement the struggling child will remember for a long time. I have also seen the inverse: the academically strong student becomes so aware of the imbalance that they deliberately underperform — making mistakes, being less thorough — to reduce the gap that makes their sibling uncomfortable.

The parents, meanwhile, are managing their own emotional responses to having children with different abilities. For parents who value maths — engineers, accountants, anyone who sees quantitative ability as practically important — having one child who struggles can activate genuine worry. That worry often gets directed at the struggling child in ways that feel supportive but are experienced as pressure. And it often gets directed away from the successful child, who receives less attention and engagement around their mathematical development precisely because they don't seem to need it. I've seen extremely able maths students coast through primary school on natural talent because the family's educational attention was entirely consumed by managing the sibling's struggles.

What works, in my observation, is deliberate compartmentalisation combined with honest acknowledgement. Compartmentalisation means giving each child a separate mathematical life within the family: separate conversations about their progress, separate goals, separate standards by which their performance is appreciated. The 68% that represents real growth for the struggling child deserves genuine celebration — not "well done despite your brother's 90%" but "well done, full stop." This requires the parents to separate their feelings about one child's performance from their feelings about the other's.

Honest acknowledgement means not pretending the gap doesn't exist, because children can see it and the pretence is patronising. "You and your brother are different at maths. That's real. What we care about is whether you're doing your best and learning something. You are." This is not the most comfortable conversation, but it's more sustaining than a false reassurance the child doesn't believe.

I also try, when I have a family with a strong and a weak maths student, to make sure each of them has a place in my classroom where they can be themselves. The struggling child needs to feel safe making mistakes and asking questions without their sibling's reputation preceding them. The strong child needs to be genuinely challenged rather than simply confirmed in their ability. Both of them deserve to be in a room where they are met as individuals.

The maths ability gap between siblings is usually not the problem. The problem is what the family builds around that gap: the stories, the comparisons, the anxiety, the management. Those are the things that determine what the gap actually costs.