My Teacher Is An AlienBook - 1989
Uneasy about her new substitute teacher, Susan Simmons' suspicions about Mr. Smith are confirmed when she discovers he is an alien determined to bring some sixth-grade specimens back to his planet
Simon and Schuster
Sixth grade is just out of this world...
Susan Simmons can tell that her new substitute teacher is really weird. But she doesn't know how weird until she catches him peeling off his face -- and she realizes that "Mr. Smith" is really an alien!
At first no one will believe her -- except Peter Thompson, the class brain. When Peter and Susan discover Mr. Smith's horrible plans for their classmates, they know they have to act fast. Only they can get rid of their extra-terrestrial visitor -- and save the rest of the sixth grade class from a fate worse than math tests!