The document discusses ability grouping in middle school mathematics classrooms. It reviews research on different types of ability grouping and their effects on student achievement. While high-ability students tend to perform slightly better in homogeneous groups, middle- and low-ability students generally achieve more in heterogeneous groups. The overall research suggests heterogeneous grouping is most effective, though there is still debate around balancing support for high-achieving students. Effective ability grouping involves flexible small groups for portions of the day rather than rigid tracking all day.