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.
Answer: The song isn't on the soundtrack, and I can't find anywhere in the film where Jack sings lyrics that even sound like Tears. I don't think it's true.