Pre-registration is required for all classes. For a class to be held, a minimum number of participants must be met, so we can cover the cost of the instructor. We ask people to register at least one week prior to the class start date, so we know what our numbers are. The numbers help the instructor structure their classes. If we do not meet our minimum requirement the class can be cancelled, that is why we do not recommend waiting until the day or night of the class start date.