Background: Test-to-stay (TTS) is a strategy to limit school exclusion following an exposure to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We evaluated the use of TTS within universally masked kindergarten through 12th grade (K-12) school settings following household SARS-CoV-2 exposure. Methods: Three hundred twenty-two participants were enrolled. Serial rapid antigen testing was performed up to 15 days post-exposure. Analysis-eligible participants completed the 15-day testing protocol, tested positive any time during the testing window, or received a negative test on or after day 9. Primary outcomes included within-school tertiary attack rate (TAR) (test positivity among close contacts of positive TTS participants), and school days saved among TTS participants. Results: Seventy-three of 265 analysis-eligible participants tested positive for SARS-CoV-2 (secondary attack rate of 28% [95% CI: 16-63%]). Among 77 within-school close contacts, 2 were positive (TAR = 3% [95% CI: 1-5%]). Participant absences were limited to 338 days, resulting in 82% of 1849 school days saved. Implications for School Health Policy, Practice, and Equity: TTS facilitates continued in-person learning and can greatly reduce the number of missed school days. Conclusions: Within universally masked K-12 schools, TTS is a safe alternative to school exclusion following household SARS-CoV-2 exposure.