This paper evaluates the Jumpstart Program (JSP), a parenting intervention implemented by a school district in the Houston area to enhance school readiness among economically disadvantaged three-year-old children. Unlike many early childhood programs typically tested in controlled research settings, JSP leverages existing school district resources for scalability and practical application. We conducted a three-year randomized controlled trial to measure the program's impact on child cognitive outcomes, parental engagement, and mechanisms of change. The results indicate improvements in children's performance on curriculum-aligned assessments and modest gains in general cognitive readiness as measured by the Bracken School Readiness Assessment. Furthermore, treatment group parents demonstrated increased reading frequency with their children, underscoring enhanced parental involvement as a crucial mechanism behind the program's success. We employed a structural model to analyze both the direct effects of JSP and its indirect effects through changes in the marginal productivity of investments or preferences via habit formation. Our analysis concludes that 75% of the program's impact is attributed to direct effects, while 25% is mediated through changes in habit formation in parental investments. Our research underscores the potential of scalable, real-world interventions to bridge socio-economic gaps in early childhood development and inform the design of effective educational policies. [Additional funding provided by the Family and Community Engagement Department of the Alief Independent School Districts.]