The data presented in this article are produced as part of the original research article entitled "Working memory training involves learning new skills" (Gathercole, Dunning, Holmes & Norris, in press). This article presents a dataset of coded features for pairs of trained and untrained working memory (WM) tasks from randomized controlled trials of WM training with active control groups. Feature coding is provided for 113 untrained WM tasks each paired with the most similar task in the training program, taken from 23 training studies. A spreadsheet provides summary information for each task pair, its transfer effect size, and coding of the following features for each task: stimulus category, stimulus domain, stimulus modality, response modality, and recall paradigm.