Although the effects of achievement goals and working memory on academic performance are well established, it is not clear whether they jointly affect academic performance. Children from Primary 4 and 6 (N = 608) were administered (a) measures of working memory and updating from the automated working memory battery and a running span task, (b) performance and mastery goal measures from the inventory of school motivation, and (c) a battery of standardised and curriculum-based mathematical tests. Both mastery and performance goals had direct (positive and negative, respectively) relations with working memory capacity. The negative relation between performance goal and mathematics was stronger for children with lower levels of mastery goal or working memory, than for those with higher levels. These findings suggest that a reduction in the availability of working memory resources may be one reason for a high performance orientation to be associated with poorer academic performance. Copyright © 2013 Taylor & Francis.