You can take the written exam without a class, but i wouldn't recommend it. Its pretty tough and you have to get 43 out of 50 correct to pass. You have to know alot of technical crap like legal uniforms and court dimensions crap as well as rules that are different from nba or street ball obviously lol. So half of it is trying to erase all the stuff you 'think' you know already.

Floor test is easy, its just basically showing you know the general principles of reffing but you have to go through a 2 year probation period after while you actually learn how to ref. I don't think anyone has actually failed the 1st floor exam

Before you get put on to high school games you get observed once more by the league assignor to make sure you know what you are doing.