The relationship of directly observed classroom behavior and teacher ratings on questionnaires with a judgemental (Conners Teacher Rating Scale) or operational format was examined for 33 boys aged 6 years 5 months to 7 years 7 months. Results showed a high degree of association between observed and rated behavior. This association did not vary with the format of the rating scales but did vary with the nature of the behavior being rated. Defiance was more reliably rated than hyperactivity or inattentiveness. Several behaviors exerted a halo effect on ratings of hyperactivity, inattentiveness, and behavior problems. In particular, defiance toward a teacher increased the likelihood that a child would be rated as hyperactive or inattentive regardless of his observed level of activity or attentiveness. These results support the validity of behavior rating scales as screening measures for hyperactivity, inattentiveness, and defiance and indicate that a child's defiance and disobedience are significant causes of misclassification.