first step : please change your name from" Blue Sadness" to "Blue Happiness".This suits you better.
Second Step: When in the lecture hall, close all the books etc, and tell yourself that you will listen to the lecture only , no other thoughts. keep telling afew times, ie., self hypnosis, condition your mind to lesten what is being told.
Third step: keep repeating the second step.
4th step: keep repeating the 3rd step .
And so on ...................