RESUMEN
Although past studies have shown an association between union instability (i.e., change in family structure) and children's aggressive behaviors, the mechanism by which this occurs is less understood. This study (n = 3,387) examined whether father and mother involvement, co-parenting support, and maternal responsiveness explained the association between union instability in early life and children's aggressive behaviors at 9 years, and whether relationship status moderated this association. Findings reveal that only co-parenting support mediated this association and only for children whose mothers divorced (not for mothers who experienced a non-marital separation), suggesting that when a divorce occurs, the relationship between partners (co-parenting) is more important than the relationship with children (parenting) for children's social adjustment.