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
There was Arithmancy, the Harry Potter wiki says that it was using numbers to predict the future. It was an elective and Harry didn’t take it.
The only other class that would have had math would be Astronomy, which was a required class for all students. The students are required to make star charts and such… Seems like rote memorization was the only thing taught. The wink says that the end of year 5 tests was filling in a blank star chart from memory.
They might get some English pointers in the dozens of essays they wrote, but since essays are graded on the length of the scroll… it becomes questionable.
I think everyone hated alchemy not because of Snape alone, but because it involves math too. Scaling the resulting doze of a potion, balancing it’s effects, predicting chemi-magical reactions of ingredients - it’s all math. And Severus was portrayed just like an average techie teaching a class of humame arts students.