Stephen S. Leff, PhD

Stephen S. Leff, PhD, is a psychologist in the Department of Child and Adolescent Psychiatry and Behavioral Sciences and co-director of the Violence Prevention Initiative at CHOP.

Areas of Expertise: Aggression and bullying prevention programming, Community-based participatory research models for intervention and measurement development, Gender and social cognitive differences in aggression
Locations: Psychiatry and Behavioral Science in University City, PA
Appointments and Referrals: 1-800-TRY-CHOP (1-800-879-2467)

  • Background

    Dr. Leff is an Associate Professor of Clinical Psychology in Pediatrics at the University of Pennsylvania School of Medicine and a Psychologist at The Children’s Hospital of Philadelphia. He is the Co-Director of the new Violence Prevention Initiative at CHOP, and is a nationally recognized leader in aggression and bullying prevention programming, relational aggression (use of rumors and social exclusion to harm others), and the community-based participatory research (CBPR) process (working with community stakeholders to integrate their perspectives into best practice programming). He has been awarded five NIH grants and a Department of Education grant to support his aggression and bullying prevention programs in the urban schools. He lectures frequently both regionally and nationally, is on the Editorial Advisory Board for two leading journals, serves on two federal Review panels, and is a member of the National Bullying Research Network. He also is an Attending Psychologist in the ADHD Program at CHOP.

  • Education and Training


    Philadelphia Child Guidance Center, Philadelphia, PA


    Children's Seashore House of The Children's Hospital of Philadelphia, Philadelphia, PA

    Board Certification

    Licensed Psychologist in PA

    Undergraduate Degree

    BA - Duke University, Durham, NC

    Graduate Degree

    PhD - University of North Carolina, Chapel Hill, NC

  • Titles and Academic Titles


    Co-Director of the Violence Prevention Initiative at The Children's Hospital of Philadelphia

    Professor of Clinical Psychology in Pediatrics, University of Pennsylvania

  • Departments and Services
  • Research Interests

    Aggression prevention programming
    Gender and social cognitive differences in aggression
    Social skills promotion

  • Publications




    Leff SS, Waasdorp TE, Waanders C, Paskewich BS. Better understanding and intervening to prevent relational aggression. In: Weist MD, Lever NA, Bradshaw CP, Owens JS, editors. Handbook of School Mental Health: Research, Training, Practice, and Policy, 2nd ed. New York: Springer; 2014. p. 171-84.



    Leff SS, Lefler EK, Khera GS, Paskewich B, Jawad AF: Preliminary examination of a cartoon-based hostile attribution bias measure for urban African American boys. American Journal of Community Psychology 49: 332-346, 2011. Read the abstract

    Leff SS, Thomas DE, Shapiro ES, Wilson K, Paskewich B, Necowitz-Hoffman B, Jawad AF: Developing and validating a new classroom climate observation assessment tool. Journal of School Violence 10: 165-184, 2011. PMCID: PMC3106103. Read the abstract