It should read COMPLIMENTARY ADMISSION FOR TEACHERS AND STUDENTS in other words it means that for teachers and students admission is free or "compliments of the house" as the saying goes. Complementary means on the contrary that the teachers and students complement or support each other.
When Charlie asks about Willy Wonka's chocolate factory, Grandpa Joe tells him lots of stories, including the one about Prince Pondicherry. He also tells Charlie about the spies, and those mysterious workers who never leave the factory.
