Background: Public preschool can provide opportunities for earlier detection of child health problems and receipt of special needs services. This is especially important for children from low-income households who disproportionately face cost barriers to obtaining health screenings and services. Objective: This study explores the possibility that entering public preschool at age 3 instead of age 4 could contribute to earlier detection of health problems and receipt of special needs services for low-income children. Method: We analyzed data on 757 low-income children in Tulsa, Oklahoma who attended Head Start or public pre-k. We compared rates of parent-reported health conditions and Individualized Education Plans (IEPs) at age 4 according to children's pattern of preschool attendance across their 3- and 4-year-old years, using propensity score-weighted logistic regressions. Results: At the spring of their 4-year-old year, children who had entered preschool at age 3 were more likely than those who entered at age 4 to have eczema (OR = 3.25, p < 0.05) and vision problems (OR = 2.26, p < 0.05). Among children who entered preschool at age 3, those who stayed in Head Start at age 4 were marginally more likely than those who transitioned to school based pre-k at age 4 to have asthma (OR = 3.81, p = 0.055) and allergies (OR = 2.16, p = 0.088). There were no differences in rates of IEPs by children's preschool experience. Conclusions: If replicated, results underscore the potentially unrealized public health benefits of expanding public preschool access to 3-year-olds.