During the summer of 2021, 80% of pediatricians reported using live audio-video telemedicine in the prior month, up from 16% of pediatricians with telemedicine experience just four years before. The child health workforce now actively uses telemedicine to care for children, but lacks evidence to guide best practices for telemedicine use in pediatric primary care. Our research team previously found gaps in the quality of care delivered by commercial direct-to-consumer telemedicine for the most common acute pediatric concerns (acute respiratory tract infections). We also demonstrated improvement in management of common chronic conditions (e.g., asthma, attention-deficit/hyperactivity disorder) using telemedicine in research settings. However, the child health community lacks data regarding the use of telemedicine in evolving “real-world” primary care practices, including how telemedicine visits compare to in- person visits for the same conditions and how telemedicine use impacts longitudinal outcomes for primary care patients. Additionally, we lack understanding of the structures and processes that support primary care practices in using telemedicine in ways that optimally enhance child health. The overarching goal of this proposal is to identify actionable strategies for promoting the use of telemedicine within primary care in ways that improve child health, using data from primary care practices from 2018-25. In Aim 1, we will compare visit-level quality of primary care visits for children delivered through telemedicine vs. in-person using electronic health record data from over 1,000 practices including independent practices, health system-affiliated practices, and community health centers. In Aim 2, we will compare child health outcomes for children receiving care in primary care practices with higher vs. lower telemedicine use through comparative interrupted time series analysis of metrics related to preventive, acute, and chronic care. Finally, in Aim 3, we will identify the practice structures and processes that promote or impede use of telemedicine in primary care in ways that improve child health through a qualitative multiple-case study. Through this rigorous mixed-methods approach informed by the Systems Engineering Initiative for Patient Safety (SEIPS) 2.0 model, we will identify visit-level and child-level impact of telemedicine integration within primary care for children as well as processes supporting health-promoting use of telemedicine. As a result, this examination of telemedicine across preventive, acute, and chronic care activities overall, for subpopulations, and within exemplar practices will provide critical knowledge to inform research, practice, and policy to optimize ongoing use of telemedicine within primary care to promote child health.