Flexible grouping aims to divide students into groups according to their strengths and abilities. This will allow teachers to tailor instruction to meet the needs of students, allowing them to thrive within their current environments. Quantitative research was used to investigate whether flexible grouping had a positive effect on student achievement as measured by the mathematics section of the Criterion-Referenced Competency Test (CRCT). The aggregate scores of students in grades 1 to 4 in a school in a county in Georgia were compared for periods before and after the implementation of flexible grouping. The following study was able to conclude that flexible grouping helps teachers closely monitor students which, in turn, allows lessons to be more catered to individual strengths and weaknesses; however, there was no direct correlation between flexible grouping and performance. There were students who performed well and others who did not. It is therefore recommended that further quantitative research based on survey and experimental designs be conducted at several other schools to corroborate or refute the results of this study for the new Georgia Milestones Mathematics Achievement Scores.