My elementary school had an awesome system; I wonder why nobody does this any more. There were four Teams (groups of classrooms) serving five grades of kids. Every Team had a mix of kids from two grades (Team 1 had first and second graders, Team 4 had fourth and fifth graders, etc.).

This meant that quick-learning kids would be able to be grouped with kids a year ahead by design, as needed, with no special scheduling required. Within each team, there were usually three classes, which meant further possibilities, as the kids moved among the classes in that team for reading or math, grouped by ability.

It really solved a lot of problems...

DeeDee