i completely agree with you! i suffer from a constant inability to pay attention. I always find myself daydreaming or messing with my friends even tho i know im missing vital info/teaching. Im in my last year at school and have struggled with this since day one. But I'm sure there is still hope! For me it is important to eat regulary, keep myself mentally stimulated by either taking notes or really thinking about what is being said. also loads of exercise helps before and after lessons. i'm lucky because during my lunch and free periods i do alot of sport, which keeps me mentally active.
i try and take every lesson as it comes, if i make myself sit through the hour and really listen (no matter how boring) i feel good at the end of it, like ive learnt something! so dont be discouraged, every1 finds it hard. keep urself active and interested, as much as possible. also its not the end of the world if u miss a few things.
hope this has answered ur question!
love leah x