Early in filming, an insecure Robert Tsai approached director Richard Linklater and tried to talk him out of letting him be in the movie because he felt he wasn't right for the role. Linklater responded that it was his very insecurity that made him exactly right for the role, and kept him in. Fittingly, Tsai's character, Lawrence, has a very similar conversation with Dewey Finn (Mr. S) about not feeling right for his role in the band.
All the kids really play their instruments, and the backup singers are real vocalists. Jack Black also played guitar in the movie (for example, when he is teaching "Smoke on the Water", "Iron Man", and other songs to Zack), but he didn't do the guitar solos.
The idea for the movie came when writer Mike White moved into an apartment next to Jack Black. White would often find Jack Black running naked through the halls or blasting much of the music featured in the movie at full volume.
Writer Mike White is actually not a huge fan of classic rock. The basis of the movie is actually used so Jack Black could perform his own favorite music.
The Mooney Suzuki: As Dewey Finn heads into the Battle of the Bands contest towards the movie's ending, he walks through a corridor and past two musicians wearing shades, leaning against a wall. The two are members of the garage rock band who provide extra instrumentation on the soundtrack.