This study evaluated direct and indirect effects of the Family Check-Up Online (FCU-O) across two distinct randomized trials with middle school youth and families. The FCU-O is a digital health adaptation of the Family Check-Up that is delivered in a brief, online format with supportive coaching. The FCU-O was delivered to parents of middle school youth with a focus on targeting both proximal and distal outcomes that impact the development of conduct problems, including a range of parenting skills, effortful control, and youth emotional problems. Participants were primary caregivers of children aged 10 to 14 years. Eligibility varied across the trials and included endorsing depression or significant stress, or having a child enrolled in a school with limited resources. A total of 374 participants across trials were included in the analysis and were randomly assigned to receive the intervention or control. Using Integrative Data Analytic techniques, we examined the effects of random assignment on a range of outcomes, including emotional and behavior problems, parenting skills, parenting confidence, and effortful control. We examined the indirect effects of the FCU-O on changes in conduct problems from baseline to 6 months via changes in mediator variables at the first follow-up assessment (2--3 months). The FCU-O improved emotional problems, effortful control, parenting confidence, and parent sense of importance at the first follow-up. Mediation analyses suggested indirect effects on conduct problems at 6-month follow-up via improvements in effortful control and emotional problems, but not via improvements in parenting confidence or sense of parenting importance. Results indicate the FCU-O has potential as a public health intervention for families with middle school youth to reduce behavioral risk. ClinicalTrials.gov Identifier: NCT 03060291; NCT 05117099.