The results referring to correlations, means, and standard deviations of the variables that composed the model tested in the study are presented in Table 1 (Correlations, means, and standard deviations of the variables that composed the final model of the study). Figure 1 (Final model with estimates in arrows) and Table 2 (Maximum likelihood estimates for the model of the effect of parental participation in the ACT Program on co-parenting and child behavior problems and child prosocial behavior) contain the main results of the model of the effect of parental participation in the ACT Program on co-parenting, child behavior problems, and child prosocial behavior. The results showed a good model fit [S-B χ² = 14129 (12), p = 0.293; Robust CFI = 0.984; Robust RMSEA = 0.058; SRMR = 0.082] (Table 1).

Post-intervention co-parenting was explained by 55.5% of the variance in the pre-intervention assessment (B = 0.712; SE = 0.082; p < 0.005, by parental participation in the ACT Program (B = 0.445; SE = 0.149; p = 0.003), these two relationships being statistically significant, in addition to the length of marital union and the quality of the marital relationship assessed at the first moment (Table 2). Regarding the child’s prosocial behaviors assessed post-intervention, the only statistically significant effect associated with it was the positive contribution of the pre-intervention assessment of the child’s prosocial behaviors (B = 0.591; SE = 0.129; p < 0.000), with 38.5% of the variance explained in the model.

Behavioral problems in children after assessment were explained by parental participation in the ACT Program in 64.6% of cases (B = -0.564; EP = 0.122; p & lt; 0.005), by co-parenting assessed at the second moment and by the child’s behavioral problems (B = 0.677; EP = 0.102; p&lt; 0.005), by prosocial behaviors and by marital union duration assessed at the first moment. Participation in the ACT Program had a statistically significant negative effect on the child’s behavioral problems (B = -0.574; SE = 0.124; p < 0.005), considering the direct effect of the intervention on the child’s behavioral problems (B = -0.564; SE = 0.122; p < 0.005) and the effect mediated by the intervention on co-parenting (B = -0.010; SE = 0.040; p = 0.802).

When considering the hypothesis of this study, the analysis of the results shows that parental participation in the ACT Program had a direct and positive impact on both co-parenting and the reduction of behavioral problems in children. However, this hypothesis was partially accepted due to the insignificant positive effect of participation in the ACT Program on children’s prosocial behaviors, as well as the absence of a statistically significant relationship between parental participation in the Program and children’s prosocial behaviors.

The direct positive effect of the ACT Program on co-parenting has been confirmed and can be explained in two complementary ways. First, several studies indicate a positive association between co-parenting and parental educational practices (Böing & Crepaldi, 2016; Feinberg & Kan, 2008; Mosmann et al., 2018). Given the effectiveness of ACT in improving parents’ educational practices (Altafim et al., 2016; Knox & Burkhart, 2014; Weymouth & Howe, 2011), it is assumed that participants shared what they learned from the Program meetings with their partners. Thus, it can be deduced that the appropriation of techniques, strategies, and general knowledge acquired had an impact on the co-parenting couple, generating a higher level of agreement, support, and improvement in the joint management of the child’s care and education. Furthermore, authors Feinberg and Kan (2008) demonstrated that parental interventions are effective strategies for improving co-parenting, which also seems to be consistent with the ACT Program.

It should be noted that, although the influence of the ACT Program on co-parenting has not yet been evaluated by other scientific studies, parental interventions provide parents with resources and strategies for emotional regulation, conflict management, and problem solving (Mejia et al., 2016). Therefore, the results of this study indicate that although the ACT Program does not specifically address the co-parenting relationship, the impacts on co-parenting are favorable and can be understood systemically, given the interdependence and dynamism between the parental, marital, and co-parenting systems, even when both parents do not participate in the intervention (Mosmann et al., 2018).

With regard to the impact of the ACT Program and/or co-parenting on children’s behavioral problems, the results showed indications of a direct reduction in children’s behavioral problems after parents participated in the Program and a total reduction when considering the direct effect of ACT combined with the effect mediated by co-parenting. However, the presumed mediating effect of co-parenting on reducing behavioral problems, when considered exclusively, was not significant.

The finding of the direct negative effect of the ACT Program on children’s behavioral problems was consistent with the findings of previous studies (Altafim et al., 2016; Burkhart et al., 2013; Knox & Burkhart, 2014). This effect is likely due to parents learning positive discipline content and strategies (Silva, 2011). The positive discipline techniques addressed during the intervention involve the importance of parents helping children resolve conflicts and identify and express emotions, positively reinforcing behaviors considered appropriate, and understanding that parents’ behavior serves as an example for children (Altafim et al., 2016; Mejia et al., 2016).

It is also assumed that increased understanding among parents about child development at different ages has enabled them to recognize normal behavior in their children, reducing expectations and encouraging more effective ways of dealing with difficult situations. Therefore, it can be inferred that changes in parental behavior were reflected in positive transformations in the child’s microsystem (Bronfenbrenner, 1996) and served as a model of interaction for the children, who, in turn, reduced behaviors considered inappropriate, based on observation and direct experience (Bandura, 1977).

The absence of a mediating effect of co-parenting on child behavior problems observed in this study is consistent with previous research linking positive co-parenting to reduced behavioral problems (Lamela, Nunes-Costa, et al., 2010; Mendez et al., 2015; Mosmann et al., 2018). In this sense, it is essential to consider that the Coparental Relationship Scale (Feinberg, Brown, et al., 2012) is designed for respondents to assess their partner’s coparenting. Thus, the findings of this study demonstrate the perception of improvement in the co-parenting relationship of the non-participating member of the couple by the person who participated in the Program. It is hypothesized that much of the reduction in children’s behavioral problems was more strongly related to the acquisition of positive educational practices than to improvements in co-parenting.

With regard to the impact of ACT and/or co-parenting on children’s prosocial behaviors, the insignificant results point to the absence of a relationship between the variables in the sample surveyed. The findings of this study did not confirm the results of a review conducted in Brazil (Altafim et al., 2016), which indicated that children’s prosocial behaviors tend to increase with parental participation in the ACT Program. It can be inferred that the explanation for the insignificant positive effect of ACT on prosocial behaviors is more closely linked to a characteristic of the sample, specifically the low average age of the children, which was around four years old. Although children already show some inclination toward prosocial actions from the age of two (Knafo-Noam, 2015), the expansion of social competence tends to occur with advancing age (Malti et al., 2013).

The factors that determine the presentation of prosocial behaviors are not yet agreed upon (Eisenberg et al., 2006), but there are indications that social competence is related both to the development of psychosocial skills throughout development and to the child’s insertion into diverse social contexts (Knafo-Noam, 2015). As children develop, empathy, the need for social acceptance (Malti et al., 2013), moral reasoning, and sense of identity are expected to increase (Carlo, 2014). Around the age of four, there is a greater tendency to begin acquiring the ability to distinguish one’s own actions from those of other people, which tends to intensify prosocial behaviors (Carlo, 2014; Souza, 2018). Furthermore, when children enter the school environment, there is commonly a tendency toward increased social competence, given the expansion of opportunities for interaction (Eisenberg et al., 2006; Malti et al., 2013).

Another possible interpretation is associated with the complexity of the prosocial behavior construct, considered a multidimensional skill that encompasses a repertoire of emotions, cognitions, and attitudes. The demonstration of prosocial behaviors is not easily identified during childhood, as it requires careful analysis on the part of the child in terms of their perception of other people’s needs and emotional reactions, as well as decision-making and problem-solving skills (Eisenberg et al., 2006). The results found by Mejia et al. (2016), based on a sample of children with an average age of six, seem to be consistent with this perspective. In this study, parents described a decrease in their children’s behavioral problems, as well as an increased ability to follow rules and instructions, after participating in a parenting training program. However, they did not observe any improvement in the child’s ability to reflect on his own behavior.

The absence of the mediating and positive effect of co-parenting, which was expected in relation to the child’s prosocial behaviors, is at odds with previous studies, which associate positive co-parenting with an increase in prosocial behaviors in children (Christopher et al., 2015; Scrimgeour et al., 2013). An important point to consider is that children’s social competence tends to be significantly affected by the microsystems involving interaction with peers, as much or more than by elements of family dynamics, including co-parenting (Eisenberg et al., 2006; Souza, 2018).

The research was a pioneer in exploring co-parenting in the context of the ACT Program, and the results indicate that even when only one parent participates, the co-parenting relationship is positively affected. This result reinforces that ACT is a promising parenting training program as a mechanism for protecting child development, given that it has the potential to positively impact not only parents’ educational practices, but also other important variables in family dynamics, such as co-parenting. In this way, not only parenting training programs with a specific focus on co-parenting, such as Family Foundations (FF) (Feinberg & Kan, 2008) and PApi (Lamela, Castro, et al., 2009), can positively intervene in improving co-parenting relationships.

The study shows that the ACT Program is effective in reducing behavioral problems in children, as already demonstrated in the literature. Regarding the limited effect on prosocial behaviors, the findings presented raise relevant questions. First, it can be assumed that prosocial behaviors during childhood are more effectively improved through the direct participation of children in social skills training with peers of the same age group. However, it is also essential to consider that the absence of impact on prosocial behaviors may be related to the need to include other variables in the statistical model. Longitudinal studies, with follow-up to monitor the impact of the intervention on pro-social behaviors in the medium and long term, may contribute to more conclusive results, given the complexity of this construct.

With regard to the expected mediating effect of co-parenting through parental participation in the intervention, which had little impact on reducing behavioral problems in children and no effect on increasing prosocial behaviors, it is considered that these results should not be treated as conclusive, precisely because of the plurality of phenomena and family subsystems that act systemically in child development. Thus, new studies face the challenge of testing other methods of data analysis. To this end, it is important to mention the need for greater paternal involvement in the ACT Program. The information obtained, whether through mixed groups or groups consisting only of men, would provide relevant information for understanding the differences, similarities, and levels of influence of fatherhood on the repercussions of the intervention.

The limitations of this study include the inability to include other sociodemographic data that could provide diverse perspectives, such as the gender and age of parents/children and educational/financial information about families. It should also be noted that the data analyzed were obtained exclusively from the parents’ reports, using the instruments and materials applied. It is understood that the use of multiple informants, such as teachers or other family members, would make the results regarding changes in the child’s behavior more robust. In the specific case of co-parenting, the response of the non-participating father would also contribute to improving understanding of the effect of this variable in the context of ACT in relation to children’s behavior.

One of the main differentiators of this study is the quality of the methodology employed, given that path analysis allows for the interrelation of several variables in a dynamic and multidirectional manner, in addition to generating data reliability. Furthermore, this method is consistent with the systemic perspective, which facilitates understanding of the interdependence between the various factors that favor or hinder child development. In this sense, systemic analysis also seems to be quite favorable for interpreting the possible transformations in parental participation in training programs such as ACT, providing support for its implementation in different contexts, including as a public mental health policy during childhood.