A previous article published in Prevention Science 3 years ago (Heinrichs et al. 2014) presented the results of a randomized controlled trial of the Triple P group program 4 years (FU4) after administration as a universal prevention approach in preschools. The present addendum resolves inconsistencies in outcome reporting (e.g., total scores of scales versus subscale scores) and provides information on measures that were additionally available to analyze further potential effects of the intervention. Effects in secondary outcome domains not reported in Heinrichs et al. (2014) are furthermore analyzed and reported. The original data analyses were varied using a different statistical model in this addendum. Re-analyses supported the original results, including changes in self-reported maternal and paternal positive parenting, in maternal dysfunctional parenting behavior as well as in maternal reports of child behavior. In addition, when analyzing the externalizing and internalizing dimensions, analysis revealed a statistically significant change in externalizing but not internalizing child symptoms. No significant intervention effects were found for secondary outcome domains. Considering important limitations in the study design [such as baseline differences at pre-assessment with mothers from intervention preschools reporting more child behavioral problems prior to introducing the intervention and predominantly non-significant effects from (a) fathers perspective, (b) teacher ratings at 1-year follow up (FU1), and (c) behavioral observations at FU1], we believe that this trial alone cannot be taken as sufficient evidence for a significant and meaningful change in child behavioral problems, which is the ultimate goal of child prevention programs. Therefore, future studies need to replicate and extend upon these results by including larger sample sizes and overcome the discussed limitations.