With me being a teenage boy in high school, there are a very limited number of thoughts that go through my head everyday. It's just easier to turn off your brain in the easier classes and make it seem like you're paying it attention but have absolutely no motivation to give a hint of effort in these classes, to talk to other people at school you might not want to, or to get to your classes on time.
Some of the thoughts I have going through my head are:
"When will this class be over?"
"Aww dang, she is attractive..."
"I wonder what we are doing for soccer today. Hopefully not conditioning.."
"Finally someone text me."
"Should I fall asleep in this class or not?"
That is only some of the thoughts I have during an average day at school. Completely mindless thoughts that a four year old could easily "up".