The role of emotional security in promoting positive adjustment following exposure to marital conflict has been identified in a large number of empirical investigations, yet to date, no interventions have explicitly addressed the processes that predict child adjustment after marital conflict. The current study evaluated a randomized controlled trial of a family intervention program aimed at promoting constructive marital conflict behaviors thereby increasing adolescent emotional security and adjustment. Families (n = 225) were randomized into 1 of 4 conditions: Parent-Adolescent (n = 75), Parent-Only (n = 75), Self-Study (n = 38) and No Treatment (n = 37). Multi-informant and multi-method assessments were conducted at baseline, post-treatment and 6-month follow-up. Effects of treatment on destructive and constructive conflict behaviors were evaluated using multilevel models where observations were nested within individuals over time. Process models assessing the impact of constructive and destructive conflict behaviors on emotional insecurity and adolescent adjustment were evaluated using path modeling. Results indicated that the treatment was effective in increasing constructive conflict behaviors (d = 0.89) and decreasing destructive conflict behaviors (d = -0.30). For the Parent-Only Group, post-test constructive conflict behaviors directly predicted lower levels of adolescent externalizing behaviors at 6-month follow-up. Post-test constructive conflict skills also indirectly affected adolescent internalizing behaviors through adolescent emotional security. These findings support the use of a brief psychoeducational intervention in improving post-treatment conflict and emotional security about interparental relationships.