I guess it depends on how the classes work. We have 4 classes but some are split into two halves (A & B) which have to be done in the right order, and the classes have to be completed in the right order too eg. once a month we have class 1,2a,3a,4a all on at the same time and the following week it would be 1, 2b,3b,4b. People need to complete 1, then 2a then 2b etc.
I initially programmed ours as one activity with the classes as different RLCs but found that I couldn't get the level of reporting and things that I wanted/needed and I didn't have room for growth - I could see it was going to get very tricky to have multiple classes at once etc. whereas doing them all as different activities in the same ministry gives plenty of room for growth and maximum reporting capacity for each classes as well as the overall picture. Plus you have the ability to register online and for people to choose which class and which date they want to take it on and I used the question and answer part of the registration to have people check a box to confirm that they are a church member (where needed) and also to check that they have completed the previous class in order to continue and register for the next (we'd then double check that in the office when the registration came through).
What I would say is think and plan it very carefully before you start as when I found it didn't do everything I needed it to and then changed the programming caused a bit of a headache, not only in the reprogramming time, but in the getting back of data later as for reports/queries I had to get results from both programming methods and put them together to get a true picture of things! Only now, almost 2 years later do I not have to keep going back to the unactive activity!
I hope this helps more and that whatever you deciced works well for you!
Blessings,
Janet