Locally my school system had what they called accelerated courses which were called AP at the senior level where you took an AP exam to get college credit. There were also L classes that were the opposite. So based on your grades and test scoring you had the choice of 3 classes but one was the simple class, one was the typical, and one was advanced. In some cases like math it would go further as you could have an senior in the freshman L class lets say. Our state had a special math and science academy that did not do grade level 9 and to get into it you had to be recommended by a teacher and apply. It was a boarding school downstate. I know it because I was recommended but did not get in. I may have never finished the application. They did not give you all that much time.