When your in class, and listening to music helps you focus thats fine to listen to it if its okay with your teacher then listen to it. Don't watch the video. If you choose to then your teacher may ask you the "RTP" (responsible thinking prosess). At that point I'd just get to doing your work, becuase well depending on the teacher they may send you down stairs, or just make you get off your computer and have it as homework and thats not too fun. But if you know yourself to get distracted from computer things (games, online chat, facebook/myspace, youtube) and you have a big assignment then just stay off them. It'll help you in the long run.