Well, when I took the course in PA 16 years or so ago it was 3 days back to back for 3-4 hours per class. Worked out great for me because I was at my grandfather's for the summer. I had been shooting for several years already and didn't need rifle time on the course. That being said, I think I was about average on being prepared for the class. At the time/location there wasn't a single kid who had never shot a gun before.
IMHO if hunters safety class is the first time your kid has shot a gun, hold off on the class and take them to a range and work them up to the gun they are going to be using. That is the only way to be sure they will be comfortable with their equipment and not screw up the shot because they are unsure about their gun. Other factors I can excuse, but being unfamiliar with your or any gun is inexcusable.