The purpose of this study was to investigate the effects of a transition to homogenous ability grouping between secondary grades on MAP test scores in an international private school in Dubai. Participants were students who have been enrolled at PISD for two years for grades 6, 7, 8, or 9 from 2020-2022 and who have presented MAP test scores both at the beginning and the end of both years. Students who attended PISD for grade 6 in 2020-2021 were in the first cohort to present comparative data in growth scores in Grade 7 during 2021-2022. Achievement growth scores were compared between end-of-year growth in 2020-2021 with heterogeneous ability grouping with end-of-year growth scores at the end of the first year using homogenous ability grouping in school year 2021-2022. After each year's first test in the fall, grades 7, 8, and 9 were divided into two groups: above-the-mean, and below-the-mean according to the whole grade's mean RIT score on the NWEA MAP test in each core subject area of math, science, reading, and language. The end-of-year growth of the two groups in each subject was compared for statistical significance. Mixed Model ANOVAs to determine significance in the interaction effect of the independent variable of converting to mixed ability grouping revealed mixed results. The null hypothesis was maintained in 10 out of 16 of the tests conducted. There was no significance in any change in end-of-year growth scores in either test for Grades 8 and 9 or Combined 7-9 Math, Grades 7 and 8 or Combined 7-9 Science, Grade 8 Reading, or all tests for Language. However, significance in the interaction effect was found in Grade 7 Math, Grade 9 Science, Grade 8 and Combined 7-9 Reading, and Grade 8 and Combined 7-9 Language. Therefore, the null hypothesis was rejected for these samples. While significance in the interaction effect was mixed across the grade levels and subject areas, what was remarkable was the trend in each group's response to homogenous grouping. The students identified as above the mean as of Fall 2021 consistently presented decreases in MAP test end-of-year growth, while students identified as below the mean presented consistent increases, and often significant increases in end-of-year growth values. The most troubling confounds to this study were the contemporaneousness to the COVID-19 pandemic and the emotional and academic set-backs students likely faced. Some teachers left mid-year during the homogenous ability grouping, possibly creating discontinuity in the assessment for learning. These confounds did not appear in the statistical analyses but are worth considering given the context of this study. Therefore, it is recommended that this study be repeated with similar methodology in a similar international school context after normal school attendance and routines are established. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]