School-based anti-bullying programs decrease victimization by 17-20% on average¶

Claim · All claims
Evidence · 1 study · quant-synthesis r? · q3
Currency · newest study 2011 · 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.

q3 i? Across 44 program evaluations, victimization decreased by 17-20% on average. → Maria M. Ttofi 2011

Evidence¶

Maria M. Ttofi 2011¶

Maria M. Ttofi, David P. Farrington. (2011). Effectiveness of school-based programs to reduce bullying: a systematic and meta-analytic review. J Exp Criminol. https://doi.org/10.1007/s11292-010-9109-1

q3 · i? · quant-synthesis · r?

Same meta-analysis of 44 evaluations from the systematic review; the pooled estimate shows "victimization decreased by 17–20%", a slightly smaller average reduction than for bullying. No standardized effect size is printed in the available text.

"on average, bullying decreased by 20–23% and victimization decreased by 17–20%"

Discussion¶

Learner Variables¶

Safety — outcome: instruction changes it

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 — related
School-based anti-bullying programs reduce bullying perpetration and victimization globally — a broader claim this one bears on
Work with peers in anti-bullying programs is associated with an increase in victimization — related
More intensive anti-bullying programs are more effective — 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
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 — related
Program effectiveness varies by country: Greece led for perpetration, Italy for victimization — related

Page metadata

Field	Value
`type`	`claim`
`id`	`anti-bullying-programs-reduce-victimization-17-20-percent`
`title`	`School-based anti-bullying programs decrease victimization by 17-20% on average`
`description`	`School-based anti-bullying programs decrease victimization by 17-20% on average`
`status`	`review`
`evidence_strength`	`moderate`
`newest_evidence`	`2011`
`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 — `maria-m-ttofi-2011`

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