We examined a number-line metaphor presented using interactive multimedia as a means of helping students build connections between an arithmetic procedure and their existing conceptual knowledge. Elementary school children learned to add and subtract signed numbers through a computer-based multimedia program over 4 training sessions. Participants received 64 example problems presented only in symbolic form (single-representation [SR] group) or in symbolic, visual, and verbal forms (multiple-representation [MR] group). In Experiment 1, compared to the SR group, the MR group (a) showed a larger pretest-to-posttest gain for high-achieving students but not for low-achieving students, (b) showed a greater gain on difficult problems but not easy problems, (c) learned faster during training, and (d) showed a greater pretest-to-posttest reduction in the use of conceptual bugs reflecting conceptually confusion between negative signs and subtraction operators. In Experiment 2, high spatial ability students in the MR group outperformed low spatial ability students on pretest-to-posttest gain. Productive learning with MRs is strongest when working memory is not overloaded, so cognitive load and MR theories can be reconciled.