Our goals in this study were to examine (a) the degree to which teacher perceptions of children's behavior in kindergarten (averaged across fall and spring for each child) predict retention by Grade 5 and (b) whether these relationships are moderated by student race, gender, or socioeconomic status (SES). Data from the Early Childhood Longitudinal Study, Kindergarten Class of 1998-99 (ECLS-K) were used to examine how Externalizing Problem Behavior (EPB; e.g., aggression, defiance) and Weak Approaches To Learning (WATL; low enthusiasm for/engagement in learning) were related to retention among children identified as Black or White (N = 6,750). Results showed that both types of behavior ratings were significant predictors of retention. There was a 46% increase in the odds of retention for every one-unit increase in EPB (OR = 1.46, p < 0.001) and a 261% increase in the odds of retention for every one-unit increase in WATL (OR = 3.61, p < 0.001). Gender moderated the relationship between EPB and retention and WATL and retention. Students who were female with EPB or WATL were at higher risk for being retained than their male peers. Implications for educators, researchers, and policymakers are discussed.