define curriculum...
in Illinois, the state sets broad standards that students are tested for, but the school district, and in some cases the individual schools, choose the specific curriculum to teach the skills needed to score well on the standardized tests
private schools (at least in Illinois) don't have to test their students, so they have more flexibility in choosing their curriculum. Many of them do test their students though, and their curricula don't differ that much from what the public schools are teaching