Few empirical studies explore how socioeconomic status (SES) disadvantaged students perform academically in a 100% online school. This causal-comparative ex post facto quantitative study examined how SES-disadvantaged students at an online charter school performed academically when compared with both SES-disadvantaged and non-SES-disadvantaged students enrolled in a traditional public school. Choice theory and how it applies to education was foundational to the study. Using archival data from 2011-2012 for math and reading on state-standardized testing, research questions compared of SES-disadvantaged students scores to non-SES disadvantaged students within two schools in one school district. The test scores analysis was by independent t-tests. The results for SES-disadvantaged students indicate significantly lower performance by online students (n = 43) compared with their counterparts at a traditional elementary school (n = 43); t = 2.33 and p = 0.022 for math and t = 3.57 and p = <0.001 for reading. Among the non-SES-disadvantaged students, results also indicate lower performance at the online charter school (n = 20) than at the traditional public school (n = 20); t = 3.22 and p = 0.003 for math and t = 2.95 and p = 0.005 for reading. No significant differences emerged between SES-disadvantaged students and non-SES disadvantaged students enrolled in the online school for math (n = 63; t = 1.65 and p = 0.105) or for reading (t = 0.89 and p = 0.378 for reading). Comparing SES-disadvantaged students and non-SES-disadvantaged students enrolled at the traditional elementary school on math scores indicated a significantly lower difference (n = 63; t = 2.58 and p = 0.012), but not on reading scores ( n = 63, t = 0.74 and p = 0.461). Additional studies should examine why online students scored lower on standardized tests. [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.]