There is a paucity of research examining the relative contribution of the different mechanisms of working memory (short-term storage [STM], processing speed) to children's complex memory span. This study served to replicate and extend the few extant studies that have examined the issue. In this study, the relative contribution of three mechanisms of working memory--STM storage, processing speed, attentional resource allocation-- to children's complex span was examined. Children (6-12) completed a digit span task, an auditory-visual reaction time task, a task of attentional allocation, and a complex (listening) span task. Correlation analyses revealed that, after controlling for age, storage, processing speed, and attentional allocation significantly correlated with complex span. Regression analyses showed that, after partialling out age, storage accounted for 12.1% of unique variance in complex span and processing speed accounted for another 6.6% of unique variance; allocation contributed no unique variance. Consistent with the developmental literature, storage and general processing speed play critical roles in children's complex span performance. (Contains 4 tables.)