In light of the difficulty in making a differential diagnosis among educable mentally retarded (EMR), emotionally handicapped (EH), and learning disabled (LD) students considering only their behavioral characteristics, a study was done to generate descriptive data regarding the behavioral characteristics of such students. Sixty EMR, EH, LD, and normal students (ages 11 and 12 years) were observed in regular classroom and resource room situations by three observers. The results indicated, among other things, that the behavior counting checklist used adequately discriminated between exceptional and normal Ss. Differences in behavioral characteristics among the three categories of exceptional Ss were also indicated. When exceptional Ss were observed in the regular classroom, their behavior was extremely variable, and a higher mean frequency of nontask oriented behavior was exhibited by all three groups. Observations in the resource room showed lower mean frequencies for nontask oriented behavior and a greater mean frequency of task oriented activity. The accuracy of measurements made by observers yielded reliability and agreement coefficients of sufficient magnitude to generalize results. (Author/DLS)