Working memory functions as an underlying force for school readiness, yet many autistic children have difficulties with it. Similarly, autistic children tend to start kindergarten with less school readiness compared with their peers. In addition, children from lower socioeconomic status (SES) backgrounds face additional barriers in working memory and school readiness. Preschool-age children with autism in the United States are entitled to pre-kindergarten (pre-K) education, yet it is unknown whether pre-K education produces long-lasting benefits in working memory. This study used a nationally representative data set to examine whether pre-K education has immediate and long-term benefits on the working memory development of children in the general sample, and whether it is particularly beneficial for autistic children's working memory development, when controlling for SES. A series of multiple regression and interaction analyses indicated that, for the general sample, having attended pre-K predicted advanced working memory during the first 2 years of elementary school (K to first grade). Particularly for autistic children, the onset of such benefits started later, in Spring of first grade, but lasted longer, until Spring of third grade (3 years). Practical implications and future directions pertaining to capitalizing on autistic children's cognitive potential and this protracted window of growth are discussed.