Stephen S. Leff, PhD

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Stephen S. Leff, PhD, is a psychologist in the Department of Pediatrics and the Department of Child and Adolescent Psychiatry and Behavioral Sciences, Co-Director of the Center for Violence Prevention at Children's Hospital of Philadelphia, and the William H. Bennett Professor of Pediatrics, University of Pennsylvania Perelman School of Medicine.

Areas of Expertise: Aggression and bullying prevention programming, Community-based participatory research models for intervention and measurement development, Racial and intersectional microaggressions, ADHD and peer relations, Gender and social cognitive differences in aggression
Appointments and Referrals: 1-800-TRY-CHOP (1-800-879-2467)


Stephen S. Leff, PhD, is the Co-Director of the Center for Violence Prevention at CHOP, a licensed Psychologist, and the William H. Bennett Professor of Psychology in Pediatrics at the Perelman School of Medicine at the University of Pennsylvania. His research focuses on aggression and bullying prevention programming, relational aggression which is the use of rumors and social exclusion to harm others, racial and intersectional microaggressions, the community-based participatory research process which is working with community stakeholders to integrate their voices and perspectives into best practice empirically-supported programming, and Scientific Edutainment which integrates empirical science with the latest entertainment technology in order to make educational programming evidence-based, engaging and relevant to youth. Dr. Leff has been the recipient of six prior NIH grants, as well as a range of other federal, local, and foundation awards to support his intervention research. He is strongly committed to issues of diversity, equity, inclusion, and anti-racism.

Education and Training


Philadelphia Child Guidance Center, Philadelphia, PA


Children's Seashore House of The Children's Hospital of Philadelphia, Philadelphia, 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 Center for Violence Prevention at Children's Hospital of Philadelphia


William H. Bennett Professor of Pediatrics, University of Pennsylvania Perelman School of Medicine

Professor of Clinical Psychology in Pediatrics and Psychiatry, Perelman School of Medicine at the University of Pennsylvania

Departments and Services

Research Interests

Aggression and bullying prevention
Community-based partnership methods for developing interventions
Racial and Intersectional Microaggressions
ADHD and peer relationships
School-based prevention

Selected Publications


Mehari KR, Beulah B, Paskewich B, Leff SS, Waasdorp TE. Cyberbullying and Empathy Among Late-Elementary School Children. Int J Bullying Prev. 2023 Mar;5(1):79-87. doi: 10.1007/s42380-022-00119-9. Epub 2022 Apr 18. PubMed PMID: 37066126; PubMed Central PMCID: PMC10103742.


*Fu R, *Leff SS, Carroll IC, Brizzolara-Dove S, Campbell K. Racial Microaggressions and Anti-Racism: A Review of the Literature With Implications for School-Based Interventions and School Psychologists. School Psychology Review. 2022 October. NIHMSID: NIHMS1853459.doi: 10.1080/2372966X.2022.2128601.  (*co-1st authors)

Puhy CE, Daly BP, Leff SS, Waasdorp TE. Identifying Relationally Aggressive Students: How Aligned are Teachers and Peers?. School Ment Health. 2022 Sep;14(3):709-723. doi: 10.1007/s12310-021-09498-8. Epub 2022 Jan 10. PubMed PMID: 37077431; PubMed Central PMCID: PMC10112531.

Waasdorp TE, Paskewich BS, Waanders C, Fu R, Leff SS. The Preventing Relational Aggression in Schools Everyday (PRAISE) Program: Adaptations to Overcome Subgroup Differences in Program Benefits. Prev Sci. 2022 May;23(4):552-562. doi: 10.1007/s11121-022-01348-6. Epub 2022 Jan 28. PubMed PMID: 35089506; PubMed Central PMCID: PMC9743486.


Fu R, Waasdorp TE, Paskewich B, Leff SS. Bullying perpetration among youth: The contributions of child disclosure and parent-teacher connection. J Fam Psychol. 2021 Apr;35(3):410-416. doi: 10.1037/fam0000791. Epub 2020 Aug 13. PubMed PMID: 32790468; NIHMSID:NIHMS1789788.

Leff SS, Waasdorp TE, Paskewich BS, Winston FK. Scaling and Disseminating Brief Bullying Prevention Programming: Strengths, Challenges, & Considerations. School Psych Rev. 2021;50(2-3):454-468. doi: 10.1080/2372966x.2020.1851612. Epub 2021 Feb 2. PubMed PMID: 35027784; PubMed Central PMCID: PMC8754421.

Serico JM, NeMoyer A, Goldstein NES, Houck M, Leff SS. A Methodological Study of Order Effects in Reporting Relational Aggression Experiences. J Interpers Violence. 2021 Mar;36(5-6):2478-2497. doi: 10.1177/0886260518760008. Epub 2018 Mar 7. PubMed PMID: 29514551.


Leff SS, Paskewich BS, Blum NJ. Exploring Early Childhood Factors as an Avenue to Address Chronic Peer Victimization. Pediatrics. 2020 May;145(5). doi: 10.1542/peds.2020-0154. Epub 2020 Apr 1. PubMed PMID: 32238447; PubMed Central PMCID: PMC7193978.

Leff SS, Waasdorp TE, Paskewich BS, Bevans KB, Winston FK. The Free2B Multi-Media Bullying Prevention Experience: An Exemplar of Scientific Edutainment. Front Psychiatry. 2020;11:679. doi: 10.3389/fpsyt.2020.00679. eCollection 2020. PubMed PMID: 32765319; PubMed Central PMCID: PMC7378812.


Polanco C, Waasdorp TE, Paskewich BS, Leff SS. Relational victimization and aggression as predictors of academic engagement and motivation. Society for Research in Child Development. 2019 March; Baltimore, MD, United States.

Mehari KR, Waasdorp TE, Leff SS. Measuring Relational and Overt Aggression by Peer Report: A Comparison of Peer Nominations and Peer Ratings. J Sch Violence. 2019;18(3):362-374. doi: 10.1080/15388220.2018.1504684. Epub 2018 Aug 23. PubMed PMID: 31462897; PubMed Central PMCID: PMC6713460.

Waasdorp TE, Monopoli WJ, Horowitz-Johnson Z, Leff SS. Peer Sympathy for Bullied Youth: Individual and Classroom Considerations. School psychology review. 2019 September; 48(3):193-206.


Goldstein NES, Giallella CL, Haney-Caron E, Peterson L, Serico J, Kemp K, Romaine CR, Zelechoski AD, Holliday SB, Kalbeitzer R, Kelley SM, Hinz H, Sallee M, Pennacchia D, Prelic A, Burkard C, Grisso T, Heilbrun K, Núñez A, Leff S, Lochman J. Juvenile Justice Anger Management (JJAM) Treatment for Girls: Results of a randomized controlled trial. Psychol Serv. 2018 Nov;15(4):386-397. doi: 10.1037/ser0000184. PubMed PMID: 30382734.

Mehari KR, Moore W, Waasdorp TE, Varney O, Berg K, Leff SS. Cyberbullying prevention: Insight and recommendations from youths, parents, and paediatricians. Child Care Health Dev. 2018 Jul;44(4):616-622. doi: 10.1111/cch.12569. Epub 2018 May 15. PubMed PMID: 29766542.




Mehari, K.R., Moore, W., Waasdorp, T.E., Varney, O., Berg, K., & Leff, S.S.: Cyberbullying Prevention: Insight and Recommendations from Youth, Parents, and Pediatricians. Child: Care, Health & Development. Page: 1-7, 2018 Notes: DOI:10.1111/cch.12569.


Leff, S.S. & Feudtner, C. : Tackling Bullying: Grounds for Encouragement and Sustained Focus. Pediatrics 139(6), June 2017 Notes: doi:


Leff, S.S., Waasdorp, T.E., & Paskewich, B.: The broader impact of Friend to Friend (F2F): Effects on teacher-student relationships, prosocial behaviors, and relationally and physically aggressive behaviors. Behavior Modification 40(4): 589-610, 2016.


Leff, S.S., Paskewich, B.S., Waasdorp, T.E., Waanders, C., Bevans, K.B., & Jawad, A.F.: Friend to Friend: A randomized trial for urban African American Relationally Aggressive Girls. Psychology of Violence 5(4): 433-443, 2015 Notes: Published online: doi:


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.

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.




Leff SS, Fu R, Varghese J. Strategies for Addressing Racial and Intersectional Microaggressions and Macroaggressions. Anger, Aggression, and Violence: Causes, Pathology and Treatments. In Martin, C., Patel, V.B. & Preedy, V.R. Springer Nature, in press.

Leff SS, Waanders C, Iyengar SS. Disruptive Behavior Disorders, Aggression, and Oppositional Defiant Disorder. Developmental-Behavioral Pediatrics. Forthcoming.


Leff, S.S., Waasdorp, T.E, & Mehari, K. R.: An Updated Review of Existing Relational Aggression Programs. In S. M. Coyne, & J. M. Ostrov (Eds.), The development of relational aggression; (pp. 283-317, Chapter xiii, 348 Pages) Oxford University Press, New York, NY. 2018 Notes:

Leff, S.S., Streit, K.V., & Paskewich, B.S.: Supporting Urban Youth through Play: Facilitating Social and Emotional Skills. Promoting Prosocial Behaviors in Children through Games and Play: Making Social Emotional Learning Fun. Laura Nabors & Renee Hawkins (eds.). Nova Science, Page: 147-175, 2018.

Bradshaw, C. P., O'Brennan, L.M., Waasdorp, T.E., Pas, E., Blumenstyk, J., Bartolo, D., & Leff, S. S.: The New Frontier: Leveraging Innovative Technologies to Prevent Bullying. Cambridge Handbook of Violence Behavior and Aggression (2nd Ed.). A. Vazsonyi, D. Flannery, & M. Delisi (eds.). Page: 724-735, 2018 Notes: 2nd edition.


Waasdorp, T.E., Horowitz-Johnson, Z., & Leff, S.S.: Cyberbullying across the lifespan: Risk factors and consequences.  Handbook of Bullying Prevention: A Lifecourse Perspective.  C.P. Bradshaw (eds.). National Association of Social Workers (NASW) Press, Page: 69-80, 2017.


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.