Pre-AP classes prepare people for AP classes, which are harder than normal.
So presumably after a pre-AP class, one would do the AP class in the next semester?
Can I ask then also, and if I'm hijacking feel free to tell me, how you are tested overall then? The education systems I know, obviously Ireland, and a little about the UK, France and Germany, are all focused on final exams that are all held together. For example, our senior cycle, from approximately 16 to 18, is a two year course where one, for all the two years, studies the mandatory subjects I mentioned (English, Irish and Maths as well as a modern European language), and as many options as one likes, three or four. The only choice is whether to sit higher level or ordinary level (or foundation for the mandatory subjects, because the whole Leaving Cert. is void without a pass in them I think), and they are the same for everyone in the country.
Continuing my curiosity, how is entry to university regulated? Here, we must meet the minimum subject requirements, normally things like a C3 (between 55% and 60%) in subjects that are relevant. For example, Chemistry for Pharmacy, Irish for a primary school teacher. Then, the best six results are converted into points. That means that if you round up the percent to the next five, you get the points value, except for 90% to 100% is always 100 points. If there is more demand than places, the people with the highest points are taken.