Your anec-data is pretty common. Most people went to high-school with a couple people who have basically the same story you describe. One of the people in my class "smoked himself stupid" over the course of sophomore and junior year. He tried to clean up his act and he cut back a lot toward the end of junior year and did manage to graduate but he was certainly not the same person. Maybe those changes would have happened regardless of the pot (he smoked at least daily), maybe not. I have no idea where he is now.