The purpose of this study was to investigate the feasibility and validity of a modified version of Buschke's missing scan methodology, the Missing Scan Task (MST), to assess working memory capacity (WMC) and cognitive control processes in preschool children 3–6 years in age. Forty typically developing monolingual English‐speaking children between 36 and 84 months in age participated in the study. The children were tested on measures of WMC (MST), verbal and nonverbal memory (NEPSY Narrative Memory and Memory for Designs subtests), and language skills (Peabody Picture Vocabulary Test, fourth edition). Children showed increased working memory capacity scores with age, as measured by the MST, with significant differences between 3‐ and 5‐year‐olds and 3‐ and 6‐year‐olds. Significant correlations were also found between the MST and language and verbal and nonverbal memory scores. MST scores still remained significantly correlated with the other measures of memory even after age and global language were accounted for in a regression analysis, demonstrating that the MST captures unique variance related specifically to WMC and cognitive control processes used to retrieve and scan information in short‐term memory (STM). The results of this study demonstrate that the MST is a feasible and valid methodology for assessing WMC in preschool children as young 3 years of age. Copyright © 2014 John Wiley & Sons, Ltd.