Jack Black leads an ensemble cast in this heartfelt and surprisingly good comedy about a washed-up guitarist who, in a fit of desperation, impersonates a school teacher and decides to form a band with his students. Directed by Richard Linklater - yes, the guy who did Boyhood and Dazed & Confused - it's soppy in parts, but it's all so good-natured and warm you can't help but watch it with a smile.