Common Core mathematics instruction presents unique challenges for students with disabilities, particularly twice-exceptional learners who may be successful problem solvers but may have difficulty articulating their reasoning process and problem-solving approaches. Moreover, as students are encouraged to engage in mathematical discourse with their peers, teachers may find it difficult to facilitate classroom conversations about problem solving approaches without the use of structured methods. This article presents the development of a research-based self-instruction problem solving strategy (i.e., REASON) that was created for a twice-exceptional learner to facilitate independence and peer interactions. It also presents a sample IEP data graph that was used for progress monitoring. Application of the REASON mnemonic strategy has potential to assist students with disabilities who are struggling with similar challenges in articulating mathematical reasoning for Common Core mathematics.