If it's other people and being near them that is causing you to sort of tune everything out... then try to JUST tune them out.

Focus on your teacher. Focus on the sound of their voice. And focus on background sounds, like the sound of the lights humming or any air conditioning. As kaliope said, focusing on all the senses helps. I fidget a lot; I tend to focus on bouncing my foot around or on playing with the pen. I also find that I doodle if I am having trouble WATCHING the person talking. So I will doodle when I listen if it isn't something I want to write down. Then I'm doing something so that I don't tune totally out and get lost in my own thoughts.