The lack of clear and manageable implementation models for individualized instruction continued to exist in high schools. Formal individualized teaching (FIT), a differentiated instructional model, was studied to determine its impact on student learning. The FIT model included analyzing student data using a Pareto analysis to identify individual student areas to strengthen, designing instruction to address identified areas, and using formative assessment to adjust instruction. Eleventh grade students in a southern rural high school were enrolled in a FIT model taught ACT preparatory course. Results concluded that student ACT composite scores significantly increased for students who had the FIT model ACT course. The results provided evidence that the FIT model was an implementable differentiated instructional model which improved student learning. [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.]