My Teacher Is an Alien is a four-book science fiction children's book series authored by Bruce Coville.
[1] The titles include: The plot is about three children, Peter Thompson, who is called a nerd, Susan Simmons, the protagonist, and school bully Duncan Dougal.
Susan eventually discovers that Mr. Smith, their teacher, is actually an orange-eyed green alien named Broxholm, who seems to be planning to abduct five students from his class to take back with him.
At the end, the heroes publicly reveal Mr. Smith to be Broxholm by having the whole school band start to play "Stars and Stripes Forever" by John Philip Sousa in the auditorium.
One day when he is using the machine he discovers an alien creature “Poot” in the classroom refrigerator, which makes him even more suspicious of his science teacher.
The book ends with the aliens agreeing to give Peter and Broxholm one last chance to find some redeeming characteristic of humanity that would save it, apparently having decided that otherwise they will destroy the Earth.
Peter, Susan, and Duncan end up together again with Kreeblim and Broxholm for My Teacher Flunked the Planet, as they decide to join their forces to defend Earth in front of the interplanetary council.