BACKGROUND: A growing body of evidence suggests that early life health and developmental outcomes can be improved through parental support programs. The objective of this project was to test the feasibility, impact, and relative cost-effectiveness of an adapted "Reach Up and Learn" program delivered through home-visiting programs as well as through center-based parenting groups on child health and development in the municipality of Boa Vista, Brazil. METHODS: A randomized, stepped-wedge design was used to roll out and evaluate the two parenting platforms in Boa Vista municipality. A total of 39 neighborhoods with a high Neighborhood Vulnerability Index were selected for the study. For the first phase of the program, nine neighborhoods were randomly selected for home visits, and two were randomly selected for the center-based parenting groups. In the second phase of the program, 10 neighborhoods were added to the home-visiting program, and eight were added to the center-based program. In the final phase of the program, the remaining 10 control areas will also be assigned to treatment. Study eligibility will be assessed through a baseline survey completed by all pregnant women in the 39 study areas. Pregnant women will be eligible to participate in the study if they are either classified as poor, were under age 20 years when they became pregnant, or if they indicate to have been exposed to domestic or sexual violence. To assess program impact, an endline survey will be conducted when children reach age 2 years. The primary study outcome is child development at age 2 years as measured by the PRIDI instrument. Secondary outcome will be infant mortality, which will be assessed linking municipal vital registration systems to the program rollout. DISCUSSION: This trial will assess the feasibility and impact of parenting programs rolled out at medium scale. The results from the trial should create evidence urgently needed for guiding Brazil's national Criança Feliz program as well as similar efforts in other countries. TRIAL REGISTRATION: ClinicalTrials.gov, ID: NCT03386747. Registered on 13 December 2017. All items of the World Health Organization Trial Registration Data Set are available in this record.