Based on Common Core Standards (2010), mathematics interventions should emphasize conceptual understanding of numbers and operations as well as fluency. For students at risk for failure, the concrete-representational-abstract (CRA) sequence and the Strategic Instruction Model (SIM) have been shown effective in teaching computation with an emphasis on conceptual understanding. No studies have investigated the effects of CRA and SIM for teaching multiplication with regrouping. Therefore, the purpose of this study was to replicate and extend the literature, teaching subtraction and multiplication with regrouping using CRA and SIM. Three students receiving tier three mathematics interventions participated. A multiple-probe across behaviors design was used to show a functional relation. All of the students demonstrated increases in fluency across all regrouping tasks.