In Woodstock, we offer pre-algebra for 7th graders who meet certain criteria (Stanford scores 90th percentile or above, 6th grade teacher recommendation) and typically 20-25% of the students in a given year sign up for the class. If successful, those students take Accelerated Algebra I (the class I
teach) in 8th grade. Sometimes a student who was not in the pre-algebra class will ask to join the algebra class and do very well. We do give high school credit for the algebra class but their grade does not get averaged into their high school Grade Point Average. (Up until 5 years ago, their grades did count toward their GPA as a "weighted" course and this gave them such a head start in class rank that other students could never hope to catch up in high school. We felt that since class rank is a high school/college priority it should not be determined by middle school performance.) We also have the occasional 7th grader who requests Acc. Algebra instead of pre-algebra or is even ready for Accelerated Geometry. This causes more of a scheduling nightmare but because we are in a shared building with the high school we can accommodate the need. Of course, this means they complete the high school accelerated curriculum in their junior year and then need to be accommodated somehow after that. (Dartmouth is close enough to be an option.)
We do not "track" our students for any other classes. We go through all kinds of scheduling gymnastics to ensure that all our pre-algebra/algebra students are evenly distributed among our core classes.
I,personally, like our system very much. I love teaching Connected Math but it is obvious that some students have outgrown what they consider to be "investigating mathematics" and are ready for the rigors of a formal algebra course.