Three experiments investigated the roles of resource-sharing and intrinsic memory demands in complex working memory span performance in 7- and 9-year-olds. In Experiment 1, the processing complexity of arithmetic operations was varied under conditions in which processing times were equivalent. Memory span did not differ as a function of processing complexity. In Experiment 2, complex memory span was assessed under three conditions designed to vary both processing and intrinsic storage demands: mental arithmetic (significant attentional demands-requires storage), odd/even judgments (significant attentional demands-no storage required), and articulatory suppression (minimal attentional demands-no storage required). The highest memory spans were found in the articulatory suppression task. Span was at an intermediate level with arithmetic processing and was lowest for processing involving odd/even judgments. This difference in memory span for processing tasks involving arithmetic processing and odd/even judgments was eliminated in Experiment 3 when the pacing requirements of the arithmetic and odd/even processing tasks were equated. The results are consistent with the view that complex memory span performance is disrupted by processing activities that divert attentional resources from storage.