Every educator's quest is to help students learn in the environment that will allow them to obtain and retain the information presented to them. In the new age of technology, more students are able to choose the environment in which they learn. This study is a quantitative comparative study of the academic performance between online and traditional high schools. The study researched the impact of learning environment on test scores in high school 9th, 10th, and 11th grade English Language Arts, as well as on graduation rate. For the purpose of this study, 19 online and 89 traditional schools in California were selected. To maximize the variance of learning environment's effect, schools in the hybrid learning environment were not included. Multivariate analysis of covariance (MANCOVA) was employed for the statistical data analysis. The results of the analysis showed a significant impact of learning environment on graduation rate but not on academic achievement. However, after the socioeconomic status was controlled, a significant impact of the learning environment was discovered on academic achievement as well as on graduation rate. Students in online instructional schools significantly performed lower than their counterparts. Recommendations based on the findings to the educational practices and policies are discussed. [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.]