Originally Posted by indigo
True ability grouping... clustering by readiness and ability... allows pupils of any age or grade level to study curriculum at the appropriate challenge level and pacing...

Yes. A thing I've noticed in schools my kids have attended is that everyone seems to start at the same place next year, regardless of last year. This means that a few kids repeat stuff and a few kids have skipped past stuff they didn't do. This approach creates problems for both of these groups.