Background: Consistent findings about the effectiveness of parent programs to prevent or reduce child maltreatment are lacking. Methods: In the present meta-analysis we synthesized findings from 27 independent samples from randomized controlled trials (RCTs) on the effectiveness of 20 different intervention programs aimed at (i) preventing the occurrence of child maltreatment in the general population or with at-risk but non-maltreating families, or (ii) reducing the incidence of child maltreatment in maltreating families. Results: A significant combined effect on maltreatment (d∈=∈0.13; N∈=∈4883) disappeared after the trim-and-fill approach that takes into account publication bias against smaller studies without significant outcomes. However, moderator analyses showed that larger effect sizes were found for more recent studies, studies with smaller samples, programs that provide parent training instead of only support, programs that target maltreating instead of at-risk families, and programs with a moderate length (6-12 months) or a moderate number of sessions (16-30). Conclusions: More RCTs are needed to further unravel which factors are associated with program effectiveness. Because currently existing programs appeared to only reduce and not prevent child maltreatment, efforts in the field of preventive intervention should also focus on the development and testing of preventive programs for families at risk for child maltreatment.