School-based anti-bullying programs reduce bullying perpetration and victimization globally¶

Claim · All claims
Evidence · 1 study · quant-synthesis r2 · q4 · i1 small
Currency · newest study 2019 · checked against its sources 2026-10-20 (automated, 1 of 1 entry) · not reviewed by a person

Subclaims¶

Reading the evidence codes

q is the design tier, i the impact, n the sample, and the kind with its r the rigour judged within that kind: what each code means.

This claim: no standardized effect is recorded in observations/ for it yet, so no benchmark reading is possible.

q4 i1 Across 100 independent evaluations, anti-bullying programs significantly reduced school-bullying perpetration (OR = 1.324) and victimization (OR = 1.248). → Hannah Gaffney 2019

Evidence¶

Hannah Gaffney 2019¶

Hannah Gaffney, David P. Farrington, & Maria M. Ttofi. (2019). Examining the Effectiveness of School-Bullying Intervention Programs Globally: a Meta-analysis. International Journal of Bullying Prevention. https://doi.org/10.1007/s42380-019-0007-4

q4 · i1 · quant-synthesis · r2

Meta-analysis of 100 independent evaluations using the multiplicative variance adjustment model, with effect sizes mostly corrected for clustering. The pooled odds ratios correspond to "an approximate reduction of 19–20% and 15–16% for bullying perpetration and victimization respectively."

"Overall, our meta-analysis found that anti-bullying programs were effective in reducing both school-bullying perpetration (OR = 1.324; 95% CI 1.27 –1.38; p < 0.001) and school-bullying victimization (OR = 1.248; 95% CI 1.27 –1.38; p < 0.001) outcomes."

Discussion¶

Learner Variables¶

Safety — outcome: instruction changes it

Program effectiveness varies by country: Greece led for perpetration, Italy for victimization — a narrower finding that bears on this claim
Effectiveness of anti-bullying programs varies significantly across evaluations (heterogeneity) — related
School-based anti-bullying programs are effective overall, decreasing bullying by 20-23% on average — a narrower finding that bears on this claim
School-based anti-bullying programs decrease victimization by 17-20% on average — a narrower finding that bears on this claim
More intensive anti-bullying programs are more effective — a narrower finding that bears on this claim
NoTrap! was the most effective program for reducing bullying victimization, while ViSC and fairplayer.manual showed non-significant negative effects — a narrower finding that bears on this claim
The Olweus Bullying Prevention Program produced the largest effect sizes for bullying perpetration, with effectiveness varying between Norway and USA evaluations — a narrower finding that bears on this claim
Parent meetings, firm disciplinary methods, and improved playground supervision are program elements associated with decreases in bullying and victimization — a narrower finding that bears on this claim
Work with peers in anti-bullying programs is associated with an increase in victimization — reports the opposite
Regional differences in program effectiveness: North America led for perpetration, Scandinavia for victimization, with no clear overall pattern — related
Anti-bullying intervention effects are weak, and RCT designs show even smaller effects than earlier meta-analyses suggested — reports the opposite

Page metadata

Field	Value
`type`	`claim`
`id`	`anti-bullying-programs-reduce-perpetration-and-victimization-globally`
`title`	`School-based anti-bullying programs reduce bullying perpetration and victimization globally`
`description`	`School-based anti-bullying programs reduce bullying perpetration and victimization globally`
`status`	`review`
`evidence_strength`	`strong`
`newest_evidence`	`2019`
`source_checked`	`2026-10-20`
`generated`	by `process:wiki-ingest` on `2026-10-15`
`trust`	unverified — no one has confirmed this page's content
`sources`	1 — `hannah-gaffney-2019`

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