The dataset contains all raw data and corresponding standard scores used for analyses considering the effect of Cogmed-working-memory training on reading and spelling in skills in children with dyslexia and low working memory. For a full description of the reading and spelling remediation program, the working memory-training, and all measures see the file '"final data wmdyslexia.pdf". The experiment design was a randomized controlled trial, using four moments of measurement for literacy skill and two moments of measurement for working memory skill, administered in a one-to-one assessment setting. Working memory skill was assessed just before working-memory training (T1) and after working-memory training (T1a). The pretest (T1) took place prior to all interventions. For reading and spelling skill, three follow-up measurements were administered after three (T2), six (T3), and nine (T4) months of reading and spelling remediation. In this document, the process of collecting data is described, followed by an overview and description of variables included in the data set.