Rapid influenza diagnostic tests (RIDTs) have variable sensitivity. In a community-based population of kindergarten through 12th grade (K-12) students, we assessed factors that may influence RIDT performance using 2,368 paired results from Sofia® Influenza A + B fluorescent immunoassay and reverse transcription polymerase chain reaction (RT-PCR). RIDT sensitivity and specificity were 76.1% (95% CI: 72.8—79.1) and 97.2% (96.2—97.9), respectively. Factors associated with sensitivity included runny nose (OR=3.0, p<0.001), nasal congestion (1.59, p=0.045), days from symptom onset (per day; 0.75; p<0.001), myalgia (0.61; p=0.014), age (per 5 years; 0.55; p=0.001), and detection of another virus (0.50; p=0.043). Understanding these factors can aid in interpreting negative results.