One or many? Which and how many parenting variables should be targeted in interventions to reduce children's externalizing behavior?

•The one- and two-format interventions cannot be considered as purely interchangeable, since their impact is different on child externalizing behavior as reported by the parents on the one hand and on child observed behavior improvement on the other hand.•The multi-method approach produces nuanced results regarding program efficacy.•With regard to the nature of the variables manipulated, parents' self-efficacy beliefs and emotion coaching practices seem to be good candidates for increasing effective behavioral changes in children.•It may be suggested that the efficacy of parenting interventions differs also according to the stimulation sequence.

This research compared the efficacy of two parenting interventions that vary according to the number and the nature of variables in reducing preschoolers' externalizing behavior (EB). The goal was to identify which parenting intervention format (one-variable versus two-variable) caused higher behavioral adjustment in children. The first was a one-variable intervention manipulating parental self-efficacy beliefs. The second was a two-variable intervention manipulating both parents' self-efficacy beliefs and emotion coaching practices. The two interventions shared exactly the same design, consisting of eight parent group sessions. Effect on children's EB and observed behaviors were evaluated through a multi-method assessment at three points (pre-test, post-test and follow-up). The results highlighted that compared to the waitlist condition, the two intervention formats tended to cause a significant reduction in children's EB reported by their parent. However, the one-variable intervention was found to lead to a greater decrease in children's EB at follow-up. The opposite was reported for children's observed behavior, which was improved to a greater extent in the two-variable intervention at post-test and follow-up. The results illustrated that interventions' format cannot be considered as purely interchangeable since their impact on children's behavior modification is different. The results are discussed for their research and clinical implications.