I would say it totally depends on which school you've had your interview with. Some schools are very open when it comes to sharing desicion after interview. Some schools don't tell us anything at all. They just ask us to wait and wait 🙁
IMHO, if they said you should hear the decision in 4 weeks after the interview and you still haven't received anything, you have the right to contact them about your status. PM me if you have any question.