Problem presentation can influence students’ understanding, choice of strategy, and accuracy. For example, the presence and type of external representation can alter performance. In this study, we examined the effect of diagrams on students’ performance in a symbolic problem domain. Sixty-one seventh-grade students solved algebraic equations with or without an accompanying diagram. The presence of diagrams increased accuracy and use of informal strategies. Overall, the benefits of diagrams found for word problems generalized to symbolic problems.