This study examined the efficacy of a brief math intervention using cognitive behaviour instruction (CBI) supplemented by a mnemonic cue system for a 5th grade student with math computation and fluency difficulties. Regrouping operations in addition and subtraction were the targeted skills. Curriculum-based measurements were conducted at the end of each session to monitor the student's response to the intervention. Pre- and post-assessment with alternate forms of Key Math-Revised were also conducted. As compared to baseline performance, there was a 48% improvement in computing regrouping problems. There was a greater effect on accuracy in computing addition than on subtraction problems requiring regrouping, based on the post-intervention assessment. The results are discussed in relation to previous intervention research incorporating CBI approaches aimed at promoting students' cognitive, metacognitive, and self-regulatory skills for proficient computation.