Cognitive strategies are important tools for children with math difficulties (MD) in learning to solve word problems. The effectiveness of strategy training, however, depends on working memory capacity (WMC). Thus, children with MD but with relatively higher WMC are more likely to benefit from strategy training, whereas children with lower WMC may have their resources overtaxed. Children in Grade 3 (N = 147) were randomly assigned to 1 of 4 conditions: (a) verbal strategies (e.g., underlining question sentence), (b) visual strategies (e.g., correctly placing numbers in diagrams), (c) verbal plus visual strategies, or (d) an untreated control. In line with the predictions, children with MD and higher WMC benefited from verbal or visual strategies relative to those in the control condition on posttest measures of problem solving, calculation, and operation span. In contrast, cognitive strategies decreased problem-solving accuracy in children with low WMC. Thus, improvement in problem solving and related measures, as well as the impairment in learning outcomes, was moderated by WMC.