Definitely makes more sense, though I don't think they call them first years either. Boys don't start at Eton or the other posh public schools till they are thirteen - third years in old money, Year 9 in new.

I did some research. Apparently he'd be an "F-blocker" and go to "div", not classes.
Incidentally:
Lower School

For two hundred years, Eton’s only classroom.

The list of slang is atrocious, and if you used all of it your readers would give up in despair, but it might help with more obvious mistakes.

Only someone who knows about the arcane system would find any problem with it now, so don't stress over it - but I did find all those terms quite a fantasy land in themselves!