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 M-CBM produced significant gains in students' achievement, specifically, for the students who were struggling with math. (Contains 2 figures.)