Measurement of aggressive behavior in early childhood is unique given that relational aggression is just developing, physical aggression is still prevalent, and both forms of aggression are relatively overt or direct. The current study had three aims. The first aim was to examine the internal reliability, validity, and correspondence of five different assessments of aggressive behavior in early childhood: parent report, teacher report, observer report, child report, and naturalistic school-based observations. The second aim was to test a one- and two-factor model of early childhood aggression using confirmatory factor analysis. The final aim of the study was to investigate gender differences among different reports of aggression. (author abstract)