Mathematics achievement continues to be an area of concern for many educators. Currently, schools struggle with effective implementation of Response to Intervention in mathematics. The purpose of this study was to determine the impact of RtI on mathematics student achievement and to identify the teacher practices that are associated with the greatest positive growth on mathematics achievement for third grade students participating in a Tier 2 Response to Intervention. A concurrent, triangulation mixed methods design collected and analyzed both qualitative and quantitative data to address the research questions. Tier 2 mathematics teachers from three campuses in a 4A district located in northeast Texas participated in interviews and observations to determine the teacher practices used during Tier 2 mathematics instruction. Additionally, a slope of growth was calculated from the district benchmark student data on the students participating in Tier 2 mathematics intervention at the three elementary campuses to determine students with the most academic growth. The researcher found three different implementation processes with varying components of Response to Intervention. The comparison of two campuses in the triangulation stage found a significant difference in the mean slope of growth. The study concluded with a number of considerations for the participating district in the implementation of Response to Intervention with procedures, teacher practices, and mathematics instruction.