For over two years, schools, teachers, students, and families across Illinois have worked to adapt instruction and learning under the ever-changing conditions wrought by COVID-19. This report, the third and final in the Learning During the Pandemic in Illinois series, investigates how much time students spent learning in-person and/or remotely during the 2020-21 school year (SY21), and how it related to students' achievement outcomes for grades 5-8. These findings are relevant for school leaders and policymakers as they implement learning recovery efforts. As detailed in the first report of this series, Trends in Instructional Modality During the 2020-21 School Year, remote instruction was not experienced evenly across schools with different student populations in Illinois. In schools serving higher proportions of White students, students spent more time learning in-person during the SY21, on average, while schools serving higher proportions of Black, Latinx, low-income, and English learner (EL) students spent more time instructing remotely. In the second report in this series, Does School Instructional Modality Predict Average School Achievement?, we showed that while all schools in Illinois declined in average test scores, schools serving grades 3-5 performed worse on standardized tests when students spent more time in remote learning. For schools serving grades 6-8 and/or 11, the relationships between learning modality and achievement were smaller and mixed. The current report builds upon the previous two. For students in grades 5-8, we dig deeper into understanding instructional modality at the level of the individual student. We ask: 1. How did the proportion of time learning in-person versus remotely vary for students in different demographic groups in Illinois? 2. Was student instructional modality in SY21 related to average student achievement, controlling for student and school characteristics? 3. Did the relationship between modality and achievement vary depending on the school that a student attended? We show that, across schools, the proportion of time students spent learning in-person was positively related to their test scores in English Language Arts (ELA) and math. [For Part 1, see ED624501. For Part 2, see ED624503.]