The purpose of this study was to investigate the Language Agression Hypothesis. This hypothesis suggests that measurable high language proficiency is associated with low observable aggression and low language proficiency is associated with high observable aggression. Consideration was also given to qualitative differences in aggressive behaviors as a function of family income, race, age, number of parents in household, and school membership. Further data on differences in free speech and its relationship to the former variable were treated. The subjects were 55 black, 25 Puerto Ricans, and 50 white male fourth, fifth and sixth graders selected from schools within the Newark public school system. Aggression was measured using an adaptation of the physical and verbal categories employed by Walter Pearce and Dahms. The vocabulary subtest of the WISC, Metropolitan Reading Test (Elementary Form), and measures of free speech were used to measure language proficiency of subjects. The results reported suggest that the language, cognitive and social factors considered in this study may, indeed, play an important role in regulating the aggressive behavior displayed in the classroom among black, Puerto Rican, and white children. Further, it appears that when these factors interact, these interactions can often explain a significant proportion of the variation of aggression. (Author/JM).