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
I mean… According to the story… Yes?
The entire Weasley clan is shown to have a depth and breadth of magical understanding that the average wizard doesn’t. They are critical players in the organization that defeats Voldemort and they rub elbows with the most famous and politically powerful wizards on a regular basis.