BackgroundDespite the rapid dissemination of parenting programs aiming to reduce and prevent violence against children (VAC) worldwide, there is limited knowledge about and evidence of the implementation of these programs at scale. This study addresses this gap by assessing the quality of delivery and impact of an evidence-based parenting program for parents/caregivers and their adolescent girls aged 9 to 14-Parenting for Lifelong Health Teens (PLH-Teens), known locally as Furaha Teens-on reducing VAC at scale in Tanzania. The study will explore participating family and staff perspectives on program implementation and examine factors associated with implementation and how implementation quality is associated with intervention outcomes when the program is delivered to approximately 50,000 parent-child dyads (N = 100,000) in schools and community centers across eight districts of Tanzania.MethodsThis mixed-methods study will answer the following research questions: (1) what is the implementation quality and fidelity of PLH-Teens at scale in Tanzania; (2) what factors are associated with the quality of delivery and implementation fidelity of PLH-Teens; (3) how are implementation quality and fidelity associated with intervention outcomes; (4) what are participant and implementing staff perspectives on the acceptability, appropriateness, feasibility, benefits, and challenges of delivering PLH-Teens in their schools and communities; (5) what is the impact of PLH-Teens on VAC and participant well-being; and (6) how much does it cost to deliver PLH-Teens at scale? Qualitative and quantitative data will be collected directly from implementers, parents/caregivers, and adolescents using pre-post questionnaires, observational assessments, cost surveys, focus groups, and interviews. Qualitative data will be analyzed thematically with the aid of NVIVO software. Quantitative data will be cleaned and analyzed using methods such as correlation, regression, and structural equation models using Stata and R. COREQ and TREND guidelines will be used, where appropriate.DiscussionFindings will provide vital insights into some of the factors related to quality implementation at scale. Lessons learned regarding the implementation of PLH-Teens at scale will be applied in Tanzania, and also in the delivery of PLH parenting programs globally.