ABSTRACT: BACKGROUND:Research is needed to evaluate the impact of implementation support interventions over and above typical efforts by community settings to deploy evidence-based prevention programs. METHODS:Enhancing Quality Interventions Promoting Healthy Sexuality is a randomized controlled trial testing Getting To Outcomes (GTO), a 2-year implementation support intervention. It compares 16 Boys and Girls Club sites implementing Making Proud Choices (MPC, control group), a structured teen pregnancy prevention evidence-based program with 16 similar sites implementing MPC augmented with GTO (intervention group). All sites received training and manuals typical for MPC. GTO has its own manuals, training, and onsite technical assistance (TA) to help practitioners complete key programming practices specified by GTO. During the first year, TA providers helped the intervention group adopt, plan, and deliver MPC. This group then received training on the evaluation and quality improvement steps of GTO, including feedback reports summarizing their data, which were used in a TA-facilitated quality improvement process that yielded revised plans for the second MPC implementation. This paper presents results regarding GTO's impact on performance of the sites (i.e., how well key programming practices were carried out), fidelity of MPC implementation, and the relationship between amount of TA support, performance, and fidelity. Performance was measured using ratings made from a standardized, structured interview conducted with participating staff at all 32 Boys and Girls Clubs sites after the first and second years of MPC implementation. Multiple elements of fidelity (adherence, classroom delivery, dosage) were assessed at all sites by observer ratings and attendance logs. RESULTS:After 2 years, the intervention sites had higher ratings of performance, adherence, and classroom delivery (dosage remained similar). Higher performance predicted greater adherence in both years. CONCLUSIONS:These findings suggest that in typical community-based settings, manuals and training common to structured EBPs may be sufficient to yield low levels of performance and moderate levels of fidelity but that systematic implementation support is needed to achieve high levels of performance and fidelity. TRIAL REGISTRATION:ClinicalTrials.gov, NCT01818791.