Intellectually gifted children tend to demonstrate especially high working memory capacity, an ability that holdsa critical role in intellectual functioning. What could explain the differences in working memory performancebetween intellectually gifted and nongifted children? We investigated this issue by measuring working memorycapacity with complex spans in a sample of 55 gifted and 55 nongifted children. Based on prior studies, weexpected the higher working memory capacity of intellectually gifted children to be driven by more effectiveexecutive control, as measured using the Attention Network Test. The findings confirmed that intellectuallygifted children had higher working memory capacity than typical children, as well as more effective executiveattention. Surprisingly, however, working memory differences between groups were not mediated by differencesin executive attention. Instead, it appears that gifted children resolve problems faster in the processing phase ofthe working memory task, which leaves them more time to refresh to-be-remembered items. This faster problemsolving speed mediated their advantage in working memory capacity. Importantly, this effect was specific tospeed on complex problems: low-level processing speed, as measured with the Attention Network Test, did notcontribute to the higher working memory capacity of gifted children.