My Math Teacher is a Vampire — Duane L. Ostler

Blake Drywater once more finds himself facing an unexpected creature in one of his classes. Because of a sudden 'neck disorder' suffered by his math teacher, Blake and his classmates have a chilling substitute. His name is Mr. Coagulate, who has a strange fascination with blood and dreams. Meanwhile Blake's former science teacher, Mr. Marlin, uses his wizard skills to annoyingly turn himself into objects in Blake's classroom--objects that talk to Blake, but which no one else can hear! But the worst is yet to come when Blake makes a very disturbing discovery. His substitute math teacher is actually a vampire, who wants to enslave and use him as an unwilling warrior in the battlefield of vampire nightmares!