Previous studies showed working memory span predicted mathematical performance. However, it was unclear whether working memory span differed amongst children with poorer performances in mathematics (PM), English literacy (PL), or in both areas (PML). 150 Primary 5 pupils participated in the study. Assignment to performance groups was based on two standardised literacy measures and a mathematical problem solving task. Children scoring at or below the 25th percentile were classified as having performed poorly in that area. Working memory capacity was measured using the Working Memory Test Battery for Children. PML had similar working memory profiles as PL, but had lower scores than PM. Children classified as PM had similar profiles as did normally achieving children. These findings suggest children with difficulties in different topic areas may not benefit equally from working memory based intervention.