Ninety-eight first grade children were observed and tested on measures of classroom behavior, task performance, and physiological arousal level. In general, sex differences were found to be minimal, and were significant on only three out of the eighteen variables investigated. Results indicated that males were rated by teachers and observers as having significantly more classroom behavior problems and as being more aggressive. Males and females scored differently on only one performance measure, that of visual discrimination, in which case females made significantly fewer errors. Measures of both tonic and phasic arousal levels failed to differentiate between the two sexes. Implications of research efforts which essentially reveal stronger similarities than differences between male and female children are discussed. (Author/MP)