Since its origins in the 1960s cognitive revolution, “short-term” or “primary” memory has developed into the more sophisticated concept of working memory, in which information is not only retained for a brief period of time, but is also manipulated and closely involved in higher order processing activities such as comprehension, problem solving, and reasoning. While the dominant model of working memory has been Baddeley and Hitch’s multiple-component model (1974; Baddeley, 2000, 2007), there are several other theoretical views including Cowan’s embedded-processes model (1988, 1999, 2005) and Ericsson and Kintsch’s long-term working memory theory (1995). Assessments of working memory in children and adults are typically grounded or validated in light of a particular theoretical viewpoint. Research with children has focused on the relationship of working memory to academic achievement. This chapter reviews how working memory has been defined, assessed, and measured in experimental and applied (i.e., educational) settings with children. In light of this review, it raises serious questions regarding the ecological validity of much current research into the measurement of working memory in the classroom.