Background: School closures were initially believed to mitigate SARS-CoV-2, but instead may have had a limited role in reducing community SARS-CoV-2 transmission. We describe a single school's experience with in-person education during the COVID-19 pandemic. Methods: From August 17, 2020 through January 23, 2021, we conducted a prospective study at a private pre-kindergarten through 12th grade (PreK-12) school in North Carolina. The school employed numerous SARS-CoV-2 mitigation measures, including mandatory masking and physical distancing without mandated laboratory screening tests. We analyzed de-identified contact tracing data collected by the school. Results: Seventy-five primary cases were reported among the 2110 students, faculty, and staff during the study period. Twenty-one (28%) of the primary cases were on-campus during their infectious periods; however, no classroom close-contacts subsequently reported a positive SARS-CoV-2 test result. Two secondary cases likely resulted from unmasked exposure at a school athletic event. There was no correlation between community incidence and secondary transmission in the school. Conclusions: Despite high rates of SARS-CoV-2 community incidence during the study period, routine mitigation practices including daily health screenings, mandatory face coverings, and efficient contact tracing contributed to minimal secondary SARS-CoV-2 transmission within an urban PreK-12 school. The limited school-associated transmission occurred when masks were not used during athletic events.