To examine the components affecting the quality of the implementation and their impact on the outcomes of the "Growing Up Happily in the Family" program targeted at parents with children aged 0–5.

At-risk and non-at-risk parents (N = 196) participated in 26 groups in local social services. Adherence, adaptations, quality of delivery, group and participant responsiveness, and implementation barriers were examined as predictors of attendance rate and changes in parental child-rearing attitudes, parental sense of competence, and parenting stress using hierarchical linear regressions analyses.

Greater participant responsiveness and fewer implementation barriers predicted higher attendance rates. These implementation variables, as well as greater program adherence, fewer crucial adaptations, and better didactic functioning of the sessions, predicted positive parental changes.

The level of implementation contributes to the program effectiveness, suggesting the need to provide a high-quality and well-coordinated implementation to achieve the intended program outcomes in child welfare populations.