“pretty decent actor”???
You’re standards must be VERY high!
What prep school? He doesn’t look like the prep-school type (I did a PG year at Lawrenceville way back when...).
It was an exercise in understatement. Acting is a profession that I generally have no respect for. Duvall is an exception.
The school is Severn School in Severna Park, MD, which is near Annapolis. Duvall's father was a Navy Admiral and the family lived in Annapolis for a while. According to his bio in Wikipedia, Duvall's mother was related to Robert E. Lee. It's not hard to see where he got his conservative credentials.
Maybe he wasn't the prep-school type, which could help explain the expulsion.