A Plague of Sorcerers: A Magical Mystery

Ok, so THIS is the long-lost book I read while volunteering at Broward County Library way back in the 90s. Finally found it!
That said, I've re-read it and it is funny and smart and the twist was an actual twist! I didn't get it until the main character revealed it (he's one smart cookie). Part of the reason I didn't recognize it (I think) is that the cover art is completely different from what I'd seen on the book I'd read. However, the local library here had the same cover art as the book I'd originally found. Excellent, no?
This book is definitely for younger readers (I'd say around the elementary to middle school range), but it's a fun light read for anyone. The sequel is on my holds list so I'll finally find out how that one is/how the story ends!!