I mean, most of the time it helps with concentration but I think the teacher should also have the right to make the students (those who aren't doing school work and are just fooling around) put it away as a sort of punishment because otherwise it would just ruin the whole point of school in the first place.
I am actually listening to music right now (I'm done with all my work), and it can keep me focused. Usually I get distracted by all the chatting and noises around the classroom. Music also keeps people quiet and not distracted. It can keep the stress off of the teachers becasue we are all doing work.
When i am doing work in school it really calms me down because I black out from the rest of the world and I just focus on my school work. I feel like teachers should let us hear music because it will actually help them, by concentrating us on our work.