It seems that it is common knowledge and courtesy to say "Bless You" after one sneezes. However in one California school, you may be docked a grade lower for saying it.
At Will C. Wood High School in Vacaville, CA, health teacher Steve Cuckovich takes off 25 points for students who reply after a sneeze. While he claims this has nothing to do with religion, Cuckovich feels that it's a disruption in the learning environment.
“It’s not… got anything to do with religion, it’s got to do with an interruption of class time. The blessing doesn’t really make any sense any more. In the old days, they thought you were dispelling evil spirits out of your body, so they were saying “God bless you” for getting rid of the evil spirits. But today I say really what you’re doing doesn’t make any sense anymore.”