Coming from Delaware, most every school, public and private, that I know of partitions students into math courses based on achievement level. They typically don't let students go "out of grade" by more than a year, but that's a sizable amount in high school (e.g., some juniors learning the same material as some freshman). I didn't know there were places that didn't do it that way-- do your local schools not have advanced math & regular math tracks for their students?