BackgroundTo prevent childhood obesity and promote healthy development, health authorities recommend that child care programs use the evidence-based practices that foster healthy eating and physical habits in children. Go NAPSACC is an intervention shown to improve use of these recommended practices, but it is known to encounter barriers that limit its impact and widespread use.MethodsThis study will use a type 3 hybrid effectiveness-implementation cluster-randomized trial to compare effectiveness and implementation outcomes achieved from Go NAPSACC delivered with a basic or enhanced implementation approach. Participants will include approximately 25 coaches from Child Care Aware of Kentucky (serving four geographic regions), 97 child care centers with a director and teacher from each and two cross-sectional samples of 485 3–4-year-old children (one recruitment at baseline, another at follow-up). Coaches will be randomly assigned to deliver Go NAPSACC using either the basic or enhanced implementation approach. “Basic Go NAPSACC” represents the traditional way of delivering Go NAPSACC. “Enhanced Go NAPSACC” incorporates preparatory and support activities before and during their Go NAPSACC work, which are guided by the Quality Implementation Framework and the Consolidated Framework for Implementation Research. Data will be collected primarily at baseline and post-intervention, with select measures continuing through 6, 12, and 24 months post-intervention. Guided largely by RE-AIM, outcomes will assess change in centers’ use of evidence-based nutrition and physical activity practices (primary, measured via observation); centers’ adoption, implementation, and maintenance of the Go NAPSACC program (assessed via website use); center directors’, teachers’, and coaches’ perceptions of contextual factors (assessed via self-report surveys); children’s eating and physical activity behaviors at child care (measured via observation and accelerometers); and cost-effectiveness (assessed via logs and expense tracking). The hypotheses anticipate that “Enhanced Go NAPSACC” will have greater effects than “Basic Go NAPSACC.”DiscussionThis study incorporates many lessons gleaned from the growing implementation science field, but also offers opportunities to address the field’s research priorities, including applying a systematic method to tailor implementation strategies, examining the processes and mechanisms through which implementation strategies produce their effects, and conducting an economic evaluation of implementation strategies.Trial RegistrationClinicalTrials.gov, NCT03938103, Registered April 8, 2019