He was abducted by Hagrid when he turned 11 so that would place him maybe around the fifth or sixth grade.
I don’t know if canonically there are math classes at Hogwarts.
The thought came to while I was watching the anime Mashle. If you are into Harry Potter and One-Punch Man I’d recommend giving it a watch.
Someone mentioned this community below; I wanted to highlight it.
Small promotion for !harrypotter@literature.cafe
Exactly what more than 5th grade math do you need in such world?
I think a lot of people forget what they learn in 5th grade math. You learn negative numbers. You learn unit conversion, fraction, prime, square roots.
Would more math help absolutely. Especially with the logic wizard seems to lack. But it is not like many people use higher level math today anyway.
What they lack is knowledge about volume and surface calculation. That is some stuff you definitely need in life. That wizards don’t need analysis or Calculus is kinda obvious.