The purpose of this study was to assess whether intervention with an integrated focus on fraction and decimal magnitude provides added value in improving rational number performance over intervention focused exclusively on fractions. We randomly assigned 4th graders with poor whole-number performance to 3 conditions: a business-as-usual control group and 2 variants of a validated fraction magnitude (FM) intervention. One variant of FM intervention included an integrated component on fraction-decimal magnitude (FM+DM); the other included a fraction applications component (FM+FAPP) to more closely mirror the validated FM intervention and to control for intervention time. Cross-classified partially-nested analyses (N=225) provided the basis for 3 conclusions. First, FM intervention improves 4th-graders' fraction understanding and applications. Second, effects of FM intervention, even without a focus on decimals, transfer to decimal number line performance. Third, an intervention component integrating fraction-decimal magnitude does not provide added value over FM intervention on fraction or decimal performance, except on decimal tasks paralleling intervention tasks. [This is the in press version of an article published in "Contemporary Educational Psychology."]