Objectives: School-based interventions aiming to intervene early in mental disorder in young people have been tested since the 1990s. Most previous reviews looked at both targeted and universal interventions; we have only compared randomized controlled trials of universal interventions, consid- ering them as an implementable preventative intervention at a public health level. We have included other outcomes of therapy, such as self- esteem, well-being, resilience, and mentalization, to also compare the effectiveness of interventions on outcomes that appear to be associated with prevention. Methods: A meta-analysis was performed of universal RCTs of school-based psychological interventions using CBT, acceptance and commitment therapy (ACT), mindfulness, and interpersonal therapy methodologies. PsycINFO, MEDLINE, and Embase were searched. The outcome data were analyzed using RevMan 5.3. Results: The data on depression are presented as follows: 1) as in the other analyses, there was evidence of a significant small effect on symptoms of depression for the interventions as a whole; and 2) this effect was maintained after 12 months overall. The data on anxiety are presented as follows: 1) overall, the effect on anxiety symptoms was also small; and 2) this small effect was slightly better maintained with anxiety ? 12 months after intervention (d ¼ 0.17 in anxiety compared with d ¼ 0.12 with depressive symptoms). Secondary outcomes are indicated as follows: 1) no trial-measured outcomes of in- terventions have been associated with relapse prevention (eg, meta-cognition or mentalization); and 2) only one trial measured other markers of recovery, such as well-being. Conclusions: 1) Universal school-based interventions appear to have a small but significant effect on depression and anxiety symptoms that are maintained ?12 months postintervention, although the amount of long-term data is small. 2) Possible markers of treatment effectiveness against relapse and of recovery, such as meta-cognition and self-esteem, are not being monitored as out- comes. 3) Other factors, such as age and type of intervention, were also involved. For example, mindfulness and use of a facilitator, who was a non- teacher with some education or training in mental health, appear significant in terms of the effectiveness of these interventions. 4) Trial quality was low overall. Further trials with large sample groups, using attention control groups as their control with a longer period of follow-up, are needed.