y school entry, 1 in 4 children shows deficits and delays in developmental outcomes such as language, communication, motor skills, and/or socioemotional health. 1,2 Thus, many children are beginning school inadequately prepared for learning and academic success. Gaps in development tend to widen vs shrink over time without intervention, 3 creating a burden on education and health systems in the form of greater government and public expenditures for remediation and special education. 4,5 Consequently, there have been efforts to identify factors, including children's screen time, 6 that may create or exacerbate disparities in early child development. Digital media and screens are now ubiquitous in the lives of children. Approximately 98% of US children aged 0 to 8 years live in a home with an internet-connected device and, on average, spend over 2 hours a day on screens. 7 This amount exceeds the recommended pediatric guideline that children spend no more than 1 hour per day viewing high-quality programming. 8,9 Although some benefits of high-quality and interactive screen time have been identified, 10-13 excessive screen time has been associated with a number of deleterious physical, behavioral, and cognitive outcomes. 14-21 While it is possible that screen time interferes with opportunities for learning and growth, it is also possible that children with delays receive more screen time to help IMPORTANCE Excessive screen time is associated with delays in development; however, it is unclear if greater screen time predicts lower performance scores on developmental screening tests or if children with poor developmental performance receive added screen time as a way to modulate challenging behavior. OBJECTIVE To assess the directional association between screen time and child development in a population of mothers and children. DESIGN, SETTING, AND PARTICIPANTS This longitudinal cohort study used a 3-wave, cross-lagged panel model in 2441 mothers and children in Calgary, Alberta, Canada, drawn from the All Our Families study. Data were available when children were aged 24, 36, and 60 months. Data were collected between