This dissertation describes a research study designed to explore whether customization of online instruction results in improved learning in a college business statistics course. The study involved utilizing computer spreadsheet technology to develop an intelligent tutoring system (ITS) designed to: a) collect and monitor individual real-time performance feedback during the delivery of the instruction, b) use logical algorithms to intelligently analyze individual strengths and weaknesses, and c) individualize learning experiences by altering the subsequent instructional content and sequencing according to individual needs. The ADDIE model of instructional design was used to develop the customized ITS. From an instructional design standpoint, this study examines whether the ADDIE model aligns with the development of customized online instructional content. The study shows the ADDIE model is an effective framework for developing customized online instruction. The study also discusses the importance of incorporating an analysis of student errors into the ADDIE model to facilitate the design of customized instruction. The effectiveness of customized instruction was evaluated by comparing the ITS with the current online instructional module, which is neither customized nor spreadsheet-based. A third, spreadsheet-based instructional module without customization was also developed to explore the incremental effects of customization on student achievement, after controlling for the spreadsheet format of instructional delivery. Other relevant factors were also controlled in the study, including previous enrollment in a statistics course, SAT or ACT math percentile, and prerequisite GPA. A posttest assessment was administered to measure the effects of customization on student achievement. The results of the study showed customization was not significantly related to student achievement after controlling for spreadsheet delivery format and relevant learner characteristics. Furthermore, customization did not result in significant differences in the proportion of students who obtained a criterion score of 70% or higher on the posttest. However, using spreadsheet technology to deliver instruction had a significant effect on both student achievement and the proportion of students obtaining the criterion score. These results indicate that although customization did not have an effect on student scores, the use of spreadsheet technology to deliver online instruction did result in significant improvement in learner achievement. [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://www.proquest.com/en-US/products/dissertations/individuals.shtml.]