Many kindergarten teachers place students in higher and lower “ability groups” to learn math and reading. Ability group placement should depend on student achievement, but critics charge that placement is biased by socioeconomic status (SES), gender, and race/ethnicity. We predict group placement in the Early Childhood Longitudinal Study of the Kindergarten class of 2010-11, using linear and ordinal regression models with classroom fixed effects. The best predictors of group placement are test scores, but girls, high-SES students, and Asian Americans receive higher placements than their test scores alone would predict. One third of students move groups during kindergarten, and some movement is predicted by changes in test scores, but high-SES students move up more than score gains would predict, and Hispanic children move up less. Net of SES and test scores, there is no bias in the placement of African American children. Differences in teacher-reported behaviors explain the higher placement of girls, but do little to explain the higher or lower placement of other groups. Although achievement is the best predictor of ability group placement, there are signs of bias.