This report examines which instructional components (e.g., visual representations, use of number lines, teaching and using of mathematical language) and study features (e.g., group size, interventionist training) may have contributed to the effectiveness of intervention. In choosing to focus on instructional components and study features, the findings have the capacity to inform state and district leaders, as well as teachers providing intervention, on which instructional components are necessary for a rational numbers intervention to be effective. Studies that were used in the meta-analysis were ones that focused on teaching rational numbers concepts to students experiencing mathematics difficulties in Grades 3 through 9. Approximately 1,500 studies were identified and screened, leaving 77 reports to be screened more in-depth for relevance. Those still eligible were then screened for rigor by applying the What Works Clearinghouse (WWC) evidence standards. A total of 26 studies with 4,237 unique participants from 30 independent samples were included in the meta-analysis. Results from the meta-analysis suggest that intervention programs devoting time to the teaching and use of mathematical language can substantially enhance outcomes. Mathematical language is a type of abstract academic language (terms such as "equivalent," "reciprocal," "circumference") that helps students learn mathematics concepts more precisely. When students understand and use mathematical language, it is believed that the students will more deeply understand the mathematics they are learning.