Competence with rational numbers is essential for mathematics proficiency in secondary mathematics. However, many students struggle with rational number concepts, and students with mathematics difficulties struggle even more. The purpose of this study was to examine the effects of an intervention that incorporated the use of explicit instruction and length models to teach the relationship between fractions and decimals to U.S. fourth-grade students with mathematics difficulties. To conduct this study, the researcher employed a multiple probe design across three intervention groups. The results of a visual analysis determined that a functional relation existed between a fraction and decimal intervention and increased performance on two dependent variables: base-10 fraction magnitude and fraction-to-decimal translation. The magnitude of change was calculated using a between-case standardized mean difference, and the results of a social validity questionnaire were presented.