The authors conduct secondary analyses of national data from the Early Childhood Longitudinal Study –Kindergarten Cohort to investigate the degree to which the racial and ethnic composition of schools is associated with use of ability grouping practices as early as kindergarten. The authors focus on within-class ability grouping for reading instruction. The authors find that this form of grouping is practiced by a majority of kindergarten teachers and schools, although frequency of use is quite varied, and some teachers and schools use it only sporadically.