Over the past fifteen years many schools have utilized aggression prevention programs. Despite these apparent advances, many programs are not examined systematically to determine the areas in which they are most effective. One reason for this is that many programs, especially those in urban under-resourced areas, do not utilize outcome measures that are sensitive to the needs of ethnic minority students. The current study illustrates how a new knowledge-based measure of social information processing and anger management techniques was designed through a partnership-based process to ensure that it would be sensitive to the needs of urban, predominately African American youngsters, while also having broad potential applicability for use as an outcome assessment tool for aggression prevention programs focusing upon social information processing. The new measure was found to have strong psychometric properties within a sample of urban predominately African American youth, as item analyses suggested that almost all items discriminate well between more and less knowledgeable individuals, that the test-retest reliability of the measure is strong, and that the measure appears to be sensitive to treatment changes over time. In addition, the overall score of this new measure is moderately associated with attributions of hostility on two measures (negative correlations) and demonstrates a low to moderate negative association with peer and teacher report measures of overt and relational aggression. More research is needed to determine the measure’s utility outside of the urban school context.