Recent research indicates that when solving algebraic story problems, adding a diagram is beneficial for seventh and eighth grade students, however, sixth graders—particularly low-achieving ones—do not benefit from the diagrams. In the present study, we further investigate the diagrammatic advantage in low-achieving pre-algebra students and examine whether and how picture algebra instruction improves diagram comprehension and use in the target population. Results replicate the lack of diagrammatic advantage in this population for two types of diagrams. Picture algebra instruction on mapping information in word problems to one type of diagrams yields improvement in both diagrammatic forms, but not story problems without diagrams; a diagrammatic advantage emerges following this instruction. Though low-achieving students may fail to use diagrammatic representations to their benefit when solving word problems, instruction on the use of one specific form may be sufficient to facilitate a more general diagrammatic advantage.