Fighting among other things. Pretty much my junior year at my home school (the regular high school I started out at) they brought me and my group of friends into the dean's office with the vice principal and the school security officer, who was a city police officer, into the office two by two and without flat out saying it more or less said their goal was to have none of us go there by the end of the year. Out of about 18 of us by the end of the year only 3 still did. Everyone either got kicked out, like me, dropped out, or was in juvie by the end of the year.
I hardly went to school though at that school and when I did I really didn't do shit. I started at the alternative high school on what should have been my senior year and barely had sophomore credits. I ended up graduating but it took me a little more than half a year extra to do so making up all the credits.