The dimensions of working memory in children and the relationships between working memory capacity, reasoning and reading ability were investigated. Simple and complex span tests were administered to 280 grade four, five and six elementary school children. Simple span tests were hypothesized to measure the capacity to temporary store information in working memory. Complex span tests were thought to reflect the simultaneous storage and processing of information. In addition, tests for reasoning, reading comprehension and reading speed were administered. Confirmatory factor analyses showed that the various tests for working memory formed one factor, which was interpreted as temporal storage capacity. The analyses revealed also that working memory and reasoning both were related to reading comprehension, but that these constructs differed in their relations to reading speed.