A class is Pro. B class is Advanced. C is intermediate. D is beginner. "minni"'s are not put into classes like the lites bikes or 450's. They are put into age divisions. 4-6, 7-11, 12-16. And other such age classes first based on the CC's of the bike they ride, then by the age at the beginning of the year, of the rider. And if you have ever actually raced motocross, then you would know this stuff.