A wise wonk once wrote that the biggest challenge facing America’s schools is the enormous variation in the academic level of students coming into any given classroom. The subject of this NBER working paper is one proposed solution to this quandary: sorting students by ability. And though conventional wisdom (and some prior research) suggests that kids in the lower-achieving groups would fare worse with such an approach, the researchers in this study concluded that sorting is beneficial for both high and low achievers—though high achievers did see larger gains than those of their lower-scoring peers (approximately 1.6 times greater). The analysis used student- and classroom- level data linked to one cohort of Dallas elementary students—amounting to roughly 9,000 children in 135 schools who progress from the third to fourth grade (in 2003–04 and 2004–05). Analysts attempt to account for unobservable ways that schools might sort (say, by student behavior) and ultimately find that three-quarters of the schools organize students along at least one dimension: Nineteen percent by prior math scores, 24 percent by prior reading scores, 28 percent by “gifted” status, 57 percent by LEP (limited English proficiency) status, and 13 percent by special-education status (further, around 40 percent sort by at least two dimensions). If schools began perfectly grouping by ability, they would see a 0.4 SD gain in student learning. While this small-scale study provides evidence that sorting is beneficial for increased test scores, school leaders must bear in mind the importance of other factors, such as the impact of homogeneous classes on classroom culture and the importance of flexible grouping (so that students move out of low-level classes after they demonstrate mastery).
SOURCE: Courtney A. Collins and Li Gan, “Does Sorting Students Improve Scores? An Analysis of Class Composition,” NBER Working Paper Series (Cambridge, MA: National Bureau of Economic Research, February 2013).