Directed by: Richard Linklater
Starring: Jack Black, Joan Cusack, Mike White, Adam Pascal
Visible crew/equipment: When the kids are playing music in the classroom and the teacher sings along with them, you can see a crewmember's shadow on the chalkboard.
Visible crew/equipment: When Dewey is talking to Ned about his job you can see a crew member reflected on the glass window.
Continuity mistake: As Zach is 'raising his goblet of rock', his hand gets a lot lower in a shot change. (00:40:10)
Trivia: All of the children are competent musicians, and they are all playing their own instruments.
Answer: It is never said but If I was to guess, they got it from the guy he was pretending to be (Ned's) information from the school office.