I know one thing that makes me lose my focus in class is long lectures. I heard somewhere once that the average person can only listen to someone talk for about a half hour before losing focus. I have also been diagnosed with ADD and find that sometimes when people are trying to explain something to me I hear them, but don't really listen to what the words mean, especially if I'm not all that interested in the topic. (or when someone is trying to teach me the rules to a new game.) If I get confused with anything I tend to stop paying attention because it all starts to sound like gibberish to me.
