The present paper reports on the development of a modified problem checklist for use in normal samples of elementary school children. The two factors, Hypersensitivity and Distractibility, replicated over male and female samples. Hypersensitivity showed a significant grade effect, with a decrease between the first and second grade for both boys and girls. In contrast, boys scored higher than girls on Distractibility and there were no grade differences. Convergent validitiy data from peer judgments, in-class activity level, physical fitness measures, standardized achievement scores, and a comparison with another teacher judgment are presented. In addition, three Behavioral Problem Checklist (Quay & Peterson, 1967) dimensions, Conduct Problem, Personality Problem, and Inadequacy--Immaturity, were developed and their relationships to the independent measures, as well as to the new dimensions, are presented. The pattern of correlations of Distractibility was quite similar for boys and girls, with both being rated as Mean-Noisy by their peers. The findings for Hypersensitivity were somewhat weaker. Distractibility and Conduct Problem scores reflected a similar pattern of correlations with other variables; in a like manner, Hypersensitivity and Personality Problem scores reflected a similar pattern of correlations with other variables. Distractibility was related to an increased activity level and Hypersensitivity was related to a decreased activity level in young boys. The total number of behavior problems was related to a decrease in activity level for young girls. Older Distractible and Hypersensitive girls showed different patterns of activity level. It is proposed that problem behavior is more complex for older children and that Distractibility may be less influenced by the usual socialization process of school than is Hypersensitivity and may have some congenital antecedents.