When Chris Herren says kids shouldn’t get mixed up with drugs and alcohol, he knows what he’s talking about. There’s a decent chance the Fall River native could have enjoyed a career in the NBA if he hadn’t been using in college. (A standout basketball player at Durfee High, Herren tested positive for drugs while playing at Boston College and, later, Fresno State.) Now 39 with his playing days behind him — there were a few forgettable seasons with the Nuggets and the Celtics — Herren travels the country talking to kids about the effect of drugs and alcohol on his own life. This week, he stopped at Dana Hall School in Wellesley, sharing some of the harrowing story covered in the book “Basketball Junkie,” and the ESPN film “Unguarded.” We’re told the students paid close attention.