Children with co-occurring internalizing and externalizing problems (MIXED children) represent a distinct aggressive subtype with negative outcomes; understanding what works for them in treatment is imperative. The success of MIXED children in some family-based programs for aggression may be attributable to collateral reductions in internalizing symptoms. The current study examined whether reductions in internalizing behaviour in MIXED children were due to reductions in maternal depression and parent-child co-rumination. Co-rumination, a dyadic interaction related to internalizing symptoms, is defined as excessively discussing problems and dwelling on negative feelings. We investigated 154 MIXED children and 49 pure externalizers who underwent Parent Management Training/Cognitive Behavioural Therapy. Mother-child co-rumination was assessed using videotaped observations of problem discussions gathered at pre-treatment, post-treatment and follow-up. We hypothesized that, at pre-treatment, mother-child co-rumination would mediate the relation between maternal depression and child internalizing problems. During treatment, we expected that co-rumination and maternal depression would predict reductions in child symptoms. Finally, we hypothesized that reductions in co-rumination would mediate the association between improvements in maternal depression and improvements in child internalizing which would, in turn, impact externalizing outcomes. Results did not support our pre-treatment and during treatment hypotheses about the role of co-rumination as a mediator. At pre-treatment, maternal depression was associated with child internalizing problems and co-rumination; co-rumination was not associated with internalizing when controlling for maternal depression. Reductions in maternal depression were associated with improvements in child internalizing and, marginally, with child externalizing, thus partially supporting our hypotheses. We also found that reductions in co-rumination impacted child externalizing, but not internalizing behaviour, again partially supporting our hypotheses regarding co-rumination changes and child symptom changes. Finally, results demonstrated that internalizing improvements affected externalizing outcomes, partially supporting our treatment-related hypothesis. Findings have implications for understanding the development and treatment of problems in MIXED children.

Children with co-occurring internalizing and externalizing problems (MIXED children) represent a distinct aggressive subtype with negative outcomes; understanding what works for them in treatment is imperative. The success of MIXED children in some family-based programs for aggression may be attributable to collateral reductions in internalizing symptoms. The current study examined whether reductions in internalizing behaviour in MIXED children were due to reductions in maternal depression and parent-child co-rumination. Co-rumination, a dyadic interaction related to internalizing symptoms, is defined as excessively discussing problems and dwelling on negative feelings. We investigated 154 MIXED children and 49 pure externalizers who underwent Parent Management Training/Cognitive Behavioural Therapy. Mother-child co-rumination was assessed using videotaped observations of problem discussions gathered at pre-treatment, post-treatment and follow-up. We hypothesized that, at pre-treatment, mother-child co-rumination would mediate the relation between maternal depression and child internalizing problems. During treatment, we expected that co-rumination and maternal depression would predict reductions in child symptoms. Finally, we hypothesized that reductions in co-rumination would mediate the association between improvements in maternal depression and improvements in child internalizing which would, in turn, impact externalizing outcomes. Results did not support our pre-treatment and during treatment hypotheses about the role of co-rumination as a mediator. At pre-treatment, maternal depression was associated with child internalizing problems and co-rumination; co-rumination was not associated with internalizing when controlling for maternal depression. Reductions in maternal depression were associated with improvements in child internalizing and, marginally, with child externalizing, thus partially supporting our hypotheses. We also found that reductions in co-rumination impacted child externalizing, but not internalizing behaviour, again partially supporting our hypotheses regarding co-rumination changes and child symptom changes. Finally, results demonstrated that internalizing improvements affected externalizing outcomes, partially supporting our treatment-related hypothesis. Findings have implications for understanding the development and treatment of problems in MIXED children.