Our district has pathways for kids to take Algebra any year between 6th and 9th grade. However, there is no attention to formal compaction. So what tends to happen for late entry into the upper pathways is that kids will take a summer course at the university to cover a missing years worth of material before sixth grade.

We've actually had the opposite problem of the above post though. Algebra II in 8th grade has not always been at the same standard as when its taught in high school due to the quality of the teachers.