For example, I grew up in Sacramento, and our public schools had a tracked program from 2nd grade. Pretty much all of us took algebra/geometry in middle school, and those who were advanced were taking precalc or calc by 9th grade. It has been a disappointing experience to learn that in the heart of silicon valley, 30+ years later, the public schools have less to offer in terms of differentiated learning and accelerated education.
BTW, I have also been talking with Bay Area parents about this, including some HNers. Would love to chat with you/your friends to know how folks are sorting this out. We've had some success and are always looking to help others do the same. Contact info in profile.