References.

How we handle evidence.

Four rules govern everything we publish.

No statistic appears without a source. If a figure cannot be attributed, it comes off the page. Several numbers repeated across this field for years turn out to be decades old and traceable to nothing, and we have removed the ones we inherited.

We say what a number actually measures. A statistic quoted without its denominator can be technically correct and still misleading, so we give the sample, the setting, and the limits alongside the finding.

We say when the research disagrees. Some questions in this field remain unsettled, and where that is true we say so on the page rather than picking the study that suits us.

We label guidance that is not research. Much of our practical advice comes from running programs rather than from a controlled study. That is legitimate, and it is not the same thing as evidence, so we mark which is which.

Federal and national data

Government surveys and nationally representative datasets.

1. Centers for Disease Control and Prevention. Youth Risk Behavior Survey, 2023. Nationally representative survey of high school students. Source for the share of students bullied on school property and the share who missed school because they did not feel safe. Cited on the homepage, Bullying 101, and Donate.
2. National Center for Education Statistics. School Crime Supplement to the National Crime Victimization Survey, 2021 to 2022. Students ages 12 to 18, grades six to 12. Source for the overall bullying rate, the grade-by-grade breakdown, the share bullied on more than one day, and the share who told an adult at school. Cited on About, Bullying 101, and the sixth grade page.
3. Centers for Disease Control and Prevention. School-level reporting on how often bullying occurs, by school type. Source for the comparison between middle, high, and elementary schools. Cited on the sixth grade page.
4. National Survey of Children's Health, analyzed by the Center for American Progress, 2017. Source for daily preschool suspensions and expulsions and the demographic breakdown. Cited on Bullying before kindergarten.

Peer-reviewed research

Published studies. Where our record of the full citation is partial, we give the finding and enough detail to locate the work rather than inventing a reference.

1. Gaffney, H., Ttofi, M.M., and Farrington, D.P. (2019). Evaluating the effectiveness of school-bullying prevention programs: an updated meta-analytical review. Aggression and Violent Behavior, 45, 111 to 133. Pooled 100 evaluations, finding bullying perpetration reduced by 19 to 20 percent and victimization by 15 to 16 percent, with substantial variation between programs and countries. Cited on Does any of this work.
2. Ttofi, M.M., and Farrington, D.P. (2011). Meta-analysis of manual-based bullying prevention programs, reporting an average reduction of about 20 percent and noting that a substantial share of programs showed no beneficial effect. Cited on Does any of this work.
3. Karna, A., Voeten, M., Little, T.D., Poskiparta, E., Kaljonen, A., and Salmivalli, C. (2011). A large-scale evaluation of the KiVa antibullying program: Grades 4 to 6. Child Development, 82(1), 311 to 330. 8,237 students across 78 schools randomly assigned to intervention or control. Cited on Does any of this work.
4. Salmivalli, C., Lagerspetz, K., Bjorkqvist, K., Osterman, K., and Kaukiainen, A. (1996), identifying six participant roles in bullying, and Salmivalli, C. (2010), Bullying and the peer group: a review, Aggression and Violent Behavior, 15, 112 to 120. The research underpinning bystander-focused prevention. Cited on Does any of this work and Bullying 101.
5. Multicentre cluster randomized controlled trial of KiVa in United Kingdom primary schools. 118 schools, 11,111 students. Victimization fell from 20.3 to 17.7 percent in intervention schools against 21.6 to 20.7 percent in comparison schools, odds ratio 0.87, confidence interval 0.78 to 0.97. Found no significant differences in bullying perpetration, school wellbeing, or emotional and behavioral problems. Cited on Does any of this work, including the null findings.
6. Hawkins, D.L., Pepler, D.J., and Craig, W.M. (2001). Naturalistic Observations of Peer Interventions in Bullying. Social Development, 10(4), 512 to 527. Observational study of 306 bullying episodes among children in grades one to six on Canadian school playgrounds. Peers were present in 88 percent of episodes and intervened in 19 percent; 57 percent of those interventions stopped the bullying within 10 seconds, and 47 percent of interventions were themselves aggressive. Cited on Bullying 101.
7. Schwartz, A.E., et al. American Educational Research Journal. New York City study comparing sixth graders across grade configurations, controlling for student background, class size, and school type. Found lower reported bullying, fighting, and gang activity among sixth graders in K to 8 and 6 to 12 schools than in standalone 6 to 8 schools. Cited on the sixth grade page.
8. Weiss, C.C., and Kipnes, L. (2006). Research on students transitioning at the end of sixth grade, reporting lower self-esteem and higher rates of being bullied compared with students who remained in the same school, alongside no significant differences in achievement, absenteeism, suspensions, or attitudes toward school. Cited on the sixth grade page.
9. Natural experiment on school transition, Child Abuse and Neglect, 2015. Study of 698 students, half transitioning from grade five to grade six and half remaining in elementary school. Found peer victimization decreasing over the transition period while bullying perpetration remained stable, with effects moderated by sex. Cited on the sixth grade page as a finding that complicates the picture.
10. Gilliam, W.S. (2005). Prekindergarteners Left Behind: Expulsion Rates in State Prekindergarten Systems. Yale University Child Study Center. Source for preschool expulsion running roughly three times the K to 12 rate, with later work reporting far higher rates in private and community child care. Cited on Bullying before kindergarten.
11. Monks, C., et al. Cross-national study of children ages four to six reporting victim rates between 15.2 and 32.4 percent and perpetrator rates between 15.2 and 25 percent, and related observational work finding bystanders present in approximately two thirds of peer victimization incidents in early childhood. Cited on Bullying before kindergarten.
12. Research on the elementary to middle school transition identifying more impersonal classes, multiple subject teachers, increased social comparison, and more concentrated victimization patterns, meaning more children bullying and fewer children targeted. Cited on the sixth grade page.

Organizational and summary sources

Research summaries and analyses from established organizations in the field.

1. National Association for the Education of Young Children. Bullying in Early Childhood. Summarizes research finding that 20.4 percent of children ages two to five had experienced physical bullying and 14.6 percent had been teased, and reporting a study of four year olds in which roughly half were involved in bullying in some role. Also the source for the finding that roles at this age are less stable than among older children. Cited on Bullying before kindergarten.
2. Research on early childhood aggression finding physical aggression peaking near age four and declining as language and self-regulation develop. Cited on Bullying before kindergarten.
3. Research on preschool suspension and expulsion finding rates associated with program characteristics including group size, staff-to-child ratio, and support available to teachers, rather than primarily with child behavior. Cited on Bullying before kindergarten.
4. Comparative research on K to 8 versus separate middle school configurations, including New York University analysis of New York City schools, reporting mixed and configuration-dependent academic results. Cited on the sixth grade page as evidence the question is unsettled.

Found an error?

If a figure on this site is wrong, out of date, or misattributed, tell us and we will correct it. Write to info@nobulliesallowed.org with the page and the problem.

We would rather be corrected than be confidently wrong in front of a parent who needed accurate information.