The Dad Who Taught His Son Maths His Way — and Why That Child Failed My Test

I've been teaching maths for fifteen years, and I can usually tell within the first few questions of marking whether a parent has been involved in teaching the method — and which parent it was.

Let me describe a specific case, with the details changed enough to protect the family involved. A P5 boy, bright and genuinely interested in maths, started doing something unusual with long multiplication. Instead of the column method we'd been practising in class, he was using a different approach — correct in outcome, but structured differently, and with a presentation that didn't match what I'd taught. He got the answers right, but when I asked him to explain his working, he couldn't. He could produce the answer, but the intermediate steps were opaque to him.

When I spoke to his parents — and I did so carefully, because I've learned to do these conversations carefully — the father explained that he'd gone to secondary school in England in the 1980s and had been taught a different long multiplication method. He'd shown it to his son because it was, he felt, more efficient. He was right about that, actually. The method is more efficient in certain ways. What it is not is compatible with the P5 curriculum, which builds toward algebraic operations that depend on a specific understanding of positional value that the column method makes explicit and his father's preferred method obscures.

His son had been successfully taught a method that gave him right answers while bypassing the conceptual understanding those right answers were meant to demonstrate. He failed my test not because he couldn't calculate, but because the questions I set were specifically designed to probe whether he understood why the calculation worked — and he didn't. He knew the trick without knowing the magic.

This is the most common version of the problem. Dad (it's usually dad, in my experience — mothers more often just ask the teacher what method is expected; I've thought about why and don't have a definitive answer) knows a method from his own schooling that differs from what we're teaching. He shows it to his child because it's what he knows, and possibly because there's something meaningful to him about passing on his own way of doing things. The child learns the method. The method sometimes works. And then the test reveals that the underlying understanding is missing.

The second version is more acute. This is the parent who genuinely doesn't agree with our method and has decided to overrule it. I had a family where the father — an engineer, highly quantitative, clearly good at maths — came to see me after his daughter's mid-year exam to tell me that the way we were teaching division was "pedagogically backwards" and that he had taught her the "correct" way. He had, in fact, taught her a valid and efficient algorithm. The problem was that she now had two competing models in her head, couldn't always identify which one was appropriate, and had started making errors she hadn't made before precisely because the conflict between the two models introduced hesitation and confusion.

I have learned to say the following thing to parents, and to say it as calmly and respectfully as I can: "Please don't teach your child a different method from the one we're using in class, unless you've spoken to me first." This request is not about territory. I genuinely don't care whether my method is the world's best method for long multiplication. What I care about is that a child who is learning can only hold one model of a procedure comfortably at a time. Two models create confusion. Confusion creates errors. Errors create discouragement.

There is a version of parental maths involvement that is genuinely helpful, and I want to be clear about what it looks like. A parent who sits with their child and asks "can you show me how you're supposed to do it?" — who engages with the school method rather than replacing it — is offering exactly the right kind of support. A parent who notices their child is stuck and emails me to ask what method I'd recommend for reinforcing understanding at home is a parent I can work with productively.

The dynamic I find most interesting, from the family systems perspective, is what paternal maths instruction says about the relationship between father and child. For many Hong Kong fathers I've met, helping their child with maths is one of the primary forms of active parental involvement they engage in — possibly because maths is a domain where confidence is easier to locate than in subjects like English composition or Chinese essay writing. There's an element of identity in the involvement: showing the son the dad's way of doing things is a form of transmission, a teaching moment that has relational significance beyond the maths itself.

I try to honour that. When I have these conversations, I don't frame it as "you're wrong." I frame it as: "your child is being taught a specific sequence of methods that build on each other, and consistency here is genuinely important. You can absolutely help — and I'd love to tell you exactly how to help in a way that reinforces what we're doing."

Most parents respond well to this. The maths is usually not what the conversation is really about. But the maths is what's showing up on the test, and that's where I meet the family.