Asthma is a chronic disease affecting nearly 6 million children in the United States and accounts for nearly 14 million missed school days. School nurses' performance of asthma management behaviors (AMBs) may reduce exacerbations, thereby decreasing emergency visits and hospitalizations and increasing attendance at school. Self-efficacy can have a positive effect on AMBs. More research is needed on the interplay between environmental factors in school nurses' work setting, self-efficacy in providing asthma care (hereafter "self-efficacy in asthma care"), and performance of AMBs. This study used a descriptive cross-sectional online survey design with practicing registered school nurses in Pennsylvania (N = 231). Data analysis included descriptive statistics, correlation tests, and multiple regression. In separate models, self-efficacy in asthma care and student-nurse ratio were significantly associated with performance of AMBs. Schools and school nurses need stronger efforts to strengthen self-efficacy in asthma care, with the goal of increasing nurses' performance of AMBs.