<p> 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&ndash;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 (<i>n</i> = 43) compared with their counterparts at a traditional elementary school (<i>n</i> = 43); <i>t</i> = 2.33 and <i>p</i> = 0.022 for math and <i> t</i> = 3.57 and <i>p</i> = &lt;0.001 for reading. Among the non-SES-disadvantaged students, results also indicate lower performance at the online charter school (<i>n</i> = 20) than at the traditional public school (<i>n</i> = 20); <i>t</i> = 3.22 and <i> p</i> = 0.003 for math and <i>t</i> = 2.95 and <i>p</i> = .005 for reading. No significant differences emerged between SES-disadvantaged students and non-SES disadvantaged students enrolled in the online school for math (<i>n</i> = 63; <i>t</i> = 1.65 and <i> p</i> = 0.105) or for reading (t = 0.89 and <i>p</i> = 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 (<i>n</i> = 63; <i>t</i> = 2.58 and <i>p</i> = 0.012), but not on reading scores (<i> n</i> = 63, <i>t</i> = 0.74 and <i>p</i> = 0.461). </p><p>