This study analyzed performance, process, and survey data of eighth graders with learning disabilities (LDs) who took the 2017 National Assessment of Educational Progress (NAEP) digital math test. Compared with students with LDs who did not receive extended time accommodations (ETA), students with LDs who received and used ETA scored significantly higher on the test, whereas students with LDs who received but did not use ETA scored significantly lower on the test. Additionally, students with LDs in the two ETA groups reported a lower level of perceived time pressure and a higher level of math interest and enjoyment than their peers who did not receive ETA. For students with LDs who received ETA, optimal performance was achieved with 50% additional time, while their peers who did not receive ETA typically performed best when utilizing most of their allotted time. The analysis of process data revealed that students with LDs who used ETA performed more actions, had a higher number of revisits, used universal design digital tools more frequently, and performed better on time-consuming items than their peers who did not receive ETA at the same level of math performance. [This paper will be published in the "Journal of Learning Disabilities."]