Many parents now use the Internet as a preferred method of accessing parenting information and support. Evidence-based behavioral parenting programs are well-suited to online delivery and have demonstrated efficacy through numerous randomized controlled trials, with parenting outcomes enhanced relative to self-directed treatment through professional support. However, more work is needed to better understand how we can maximize treatment effects and ensure users are provided with a minimally sufficient level of support. Developing a clearer understanding of the pathways of change is an important step toward this goal. In this study, we used path analysis to examine whether measurable and modifiable factors such as a parent’s initial level of distress can predict response to online treatment both with and without professional support, and explored its impact on the putative mediating pathway of self-efficacy as a key mechanism of reductions in negative parenting. Finally, we examined the hypothesis that professional consultations were primarily responsible for improving outcomes through increasing program engagement, likely due to added accountability and its impact on motivation. Hypotheses were partially supported, showing that self-efficacy was associated with the treatment → negative parenting pathway when parents were provided with professional support, whereas in the absence of support, this pathway was disrupted for parents experiencing high levels of distress before treatment. Additionally, a plausible model was developed showing that telephone consultations influenced program engagement, but had additional effects on negative parenting not explained by the online modules alone. Clinical implications for the online delivery of parenting programs are discussed.