The purpose of this study was to explore the variations in students' achievement on computational fluency assessments and variations in strategies for solving computation problems. Computational fluency was defined as a student's ability to compute flexibly, accurately, efficiently, and appropriately. Seven- and eight-year-old students completed four paper-pencil assessments and participated in four interviews about their strategies for solving computation problems. Researchers used a mixed methods design using test scores and interviews that measured six students' development of computational fluency at four time points over nine weeks. The results showed that there was variation in students' assessment scores and strategy use, and the quantitative and qualitative data converged or diverged at various measurement points. The divergent results highlighted a trend of improved strategy use in the interviews parallel to a decrease in test scores. Implications for mathematics teachers are discussed.