This research study investigated the effects of preschool dosage on kindergarten readiness in an urban school district (n= 1,464). This study was guided by one research question: do children who attend two years of structured early childhood education programming (3-year-old and 4-year-old pre-k) demonstrate stronger academic skills than their peers who only attend one year of pre-k programming (4-year-old pre-k only)? Implementing univariate and multivariate logistic regression models, we found that children who attend two years of programming were 34% more likely to make a successful transition to kindergarten compared to their peers who only attended pre-k as 4-year-olds. Black students who attended two years experienced a greater benefit, with a 53% increased likelihood of being kindergarten-ready.