No, you don't need a previous class, but hey, nobody knows your needs better than yourself.

It would be great if you just pick up some books and start reading on the subject, and do all the class work.

The CCNA is basically memory, so don't worry too much, just remember, be smart when answering and memorize as much as you can. Later you will find other certifications that test your ability and problem solving capabilities, but the first CCNA is easy.

Trust me!!

(BTW, I don't even think you need to go to school for it!!)