Richard Dreyfuss in 'Mr Holland's Opus'. There's a Belgian film called 'The Music Teacher' directed by Gerard Corbiau. I'm sure there are music teaching scenes in 'Au Revoir les Enfants' (Irene Jacob is a piano teacher) and Jan Sverak's 'The Elementary School' but this other one may only be a brief display by the egocentric teacher. 'Un Couer en Hiver' doesn't exactly have a teaching scene but it does explore the idea of mentor and student somewhat. They're all I can think of off at the moment.