The main goals of the study were to replicate and measure the test-retest reliability of a previously used preschool working memory task, to analyze the relationship between working memory and school readiness above and beyond attention and an indicator of overall development, and to investigate these relationships for gender differences. Participants included 40 (20 girls and 20 boys) 3- and 4-year olds, and testing was broken into two sessions spaced 1 week apart. The test-retest reliability of preschool working memory was found to be r = 0.60. Further analyses demonstrated that while attention and working memory were significantly correlated with one another, working memory was a significant predictor of school readiness above and beyond the predictive ability of children's sustained attention. Specifically, for boys, working memory was a significant predictor of school readiness above and beyond both attention and developmental status, but this was not the case for girls. These findings highlight the utility of this preschool working memory methodology as well as the importance of working memory above and beyond other related constructs at this stage of child development. Additionally, and perhaps worthy of consideration in future research, these findings also suggest notable gender-based differences in working memory during the preschool period.