Working memory (WM) is recognised as universally foundational to children’s learning. While computerised training programmes can increase working memory capacity, their application in school contexts may be limited by resources and pedagogy, which may restrict use to pupils with the greatest difficulty. This research presents findings from a preliminary evaluation into the effectiveness of a novel, six-week, whole-class working memory programme, which involved pairs of children undertaking daily card-based activities within a single mainstream primary school classroom, involving 24 eight- and nine-year-old children. Post and follow-up measures demonstrated significant gains in children’s working memory and verbal short-term memory, with large effect sizes. While promising, these results should be interpreted with caution due to the sample size and age of participants. Before it can be concluded that this working memory training programme holds potential to increase children’s capacity to learn and achieve, further research needs to establish its usefulness for children with the most prominent WM difficulties, justify its application for children without WM difficulties and eliminate the possibility that gains could have occurred as a result of task-specific learning.