Dr. Leff has been in the principal investigator on five NIH grants, published a number of articles on relational aggression in African American girls, has developed cartoon-based and video based measures of the hostile attribution bias and social information processing, and has designed and implemented two relational aggression programs for high risk African American youth. Dr. Leff is also a Co-Investigator for the CDC-funded Philadelphia Collaborative Violence Prevention Center (PCVPC) for which he is the principal investigator of the five year Centerpiece Project to develop a comprehensive community-based violence prevention intervention in after-school sites within West and Southwest Philadelphia.