Aren't they all, though?
All fun aside, My Teacher Is an Alien is a series of four books written by Bruce Coville back in early 90s and includes My Teacher is an Alien (1989), My Teacher Fried my Brains (1991), My Teacher Glows in the Dark (1991) and My Teacher Flunked the Planet (1992).
The plot of each book centers around three all-American kids (Peter, Susan, Duncan) who uncover what they think is a plot to take over the world, led by their teacher Mr. Smith. Smith is eventually exposed as an alien and is forced to flee. One of the kids, Peter, decides to tag along for the and a series of space adventures ensue. Each book in the series offers the reader an interesting enough sci-fi slant that, along with the school yard vignette, will appeal to readers young and old alike.
The real treat here though, and the reason I remember the series so well, is the cover artwork. Illustrated by Mike Wimmer, each cover (with exception to the last book) showcases a different, deadly alien revealed as they pull back the "flesh" of their false face. Its a creepy cool effect that even now makes me want to crack open a copy of any one of the books.
As an added flashback bonus, I also discovered another book by Coville and Wimmer called The Monster's Ring about a boy who can become a monster with a magic ring. Its an interesting premise and one I wouldn't mind reading a little more about snuggled up with a My Pet Monster and tall glass of milk.
What a great series indeed, sir! I was thinking of doing a piece on the Goosebump series. I love how in every rendering there is someone taking their face mask off ha ha. Gotta love it!