Background: Depression is common in young people, has a marked negative impact and is associated with self-harm and suicide. Preventing its onset would be an important advance in public health.

Objectives: To determine whether psychological or educational interventions, or both, are effective in preventing the onset of depressive disorder in children and adolescents.

Search methods: The Cochrane Depression, Anxiety and Neurosis Review Group's trials registers (CCDANCTR) were searched at the editorial base in July 2010. Update searches of MEDLINE, EMBASE, PsycINFO and ERIC were conducted by the authors in September 2009. Conference abstracts, reference lists of included studies and reviews were searched and experts in the field contacted.

Selection criteria: Randomised controlled trials of psychological or educational prevention programmes, or both, compared with placebo, any comparison intervention, or no intervention for young people aged 5 to 19 years-old, who did not currently meet diagnostic criteria for depression or who were below the clinical range on standardised, validated, and reliable rating scales of depression, or both, were included.

Data collection and analysis: Two authors independently assessed studies for inclusion and rated their quality. Sample sizes were adjusted to take account of cluster designs and multiple comparisons. We contacted study authors for additional information where needed.

Main results: Fifty-three studies including 14,406 participants were included in the analysis. There were only six studies with clear allocation concealment, participants and assessors were mostly not blind to the intervention or blinding was unclear so that the overall risk of bias was moderately high. Sixteen studies including 3240 participants reported outcomes on depressive diagnosis. The risk of having a depressive disorder post-intervention was reduced immediately compared with no intervention (15 studies; 3115 participants risk difference (RD) -0.09; 95% confidence interval (CI) -0.14 to -0.05; P<0.0003), at three to nine months (14 studies; 1842 participants; RD -0.11; 95% CI -0.16 to -0.06) and at 12 months (10 studies; 1750 participants; RD -0.06; 95% CI -0.11 to -0.01). There was no evidence for continued efficacy at 24 months (eight studies; 2084 participant; RD -0.01; 95% CI -0.04 to 0.03) but limited evidence of efficacy at 36 months (two studies; 464 participants; RD -0.10; 95% CI -0.19 to -0.02). There was significant heterogeneity in all these findings. There was no evidence of efficacy in the few studies that compared intervention with placebo or attention controls.

Authors' conclusions: There is some evidence from this review that targeted and universal depression prevention programmes may prevent the onset of depressive disorders compared with no intervention. However, allocation concealment is unclear in most studies, and there is heterogeneity in the findings. The persistence of findings suggests that this is real and not a placebo effect.