Kindergarten unreadiness for children in poverty contributes to an early and persistent achievement gap in elementary school that can evolve into an opportunity gap in adulthood. This study explored the effect of the federally funded Preschool Development Grant program on school readiness for marginalized children in Southern Arizona. The theoretical framework of this study was based on early childhood development theory and the work of Piaget, Montessori, and Bloom. The tenets of early childhood development theory also guided curriculum and practice for teachers in the PDG program. The sample consisted of twenty-six kindergarten students, a much smaller sample than the projected number of eighty, due to COVID-19 school closures. Thirteen students in the sample attended a full year of the PDG program. Thirteen students, of like socio-economic background, arrived in kindergarten without preschool experience of any kind. This quantitative comparative study drew data from archived early reading scores from the Fastbridge reading assessment and scores reflecting social-emotional skill levels from BASC-3 teacher surveys. Mann Whitney U t-tests were run through SPSS to compare the scores of both groups. The null hypotheses that a year in the PDG program would have no significant effect on school readiness for marginalized children in Southern Arizona could not be rejected. The results showed no significant effect on school readiness for the thirteen students that received the treatment of a year in the PDG program. The sample may have been too small and/or kindergarten may have been too early to check for an effect. There is a need for further research to explore which programs do have a positive effect on children of this demographic and to inform curriculum and best practices in the future. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]