The proper assessment of math computational skills is essential for monitoring progress, predicting achievement, and identifying students with disabilities. The current study extends previous research on assessment of curriculum-based measurement in mathematics(M-CBM) . The purpose of this research was to examine the effects of the M-CBM computation assessment on improving third-grade math achievement. This paper presents a comparison study of two classrooms; one used a M-CBM computation in addition to the summative assessment and one used summative assessment only. Each class consisted of 35 students; three who had a Specific Learning Disability in math. The results of a 15-week CBM process demonstrated the effectiveness of using the M-CBM with third- grade students. Furthermore, when compared to the traditional way of assessment, the use of the MCBM produced significant gains in students’ achievement, specifically, for the students who were struggling with math.