The Harry Potter series by J.K. Rowling. Now THIS is the greatest series ever written. I really need to just buy the series...it's been years since I've read them...the first one I read 12 or 13 years ago!
The Worst Witch by Jill Murphy. I don't think this was the version I read back in the very early 1980s, but never mind
Enid Blyton's Mallory Towers - the 9 year old me was sad to discover this was not a real school!