OBJECTIVE. We aimed to determine the effectiveness of school-based supervised asthma therapy in improving asthma control. The primary hypothesis was that the supervised-therapy group would have a smaller proportion of children experiencing an episode of poor asthma control each month, compared with those in the usual-care group. METHODS. Children were eligible if they had physician-diagnosed persistent asthma, the need for daily controller medication, and the ability to use a dry-powder inhaler and a peak flowmeter. The trial used a 2-group, randomized, longitudinal design with a 15-month follow-up period. A total of 290 children from 36 schools were assigned randomly to either school-based, supervised therapy or usual care. Ninety-one percent of the children were black, and 57% were male. The mean age was 11 years (SD: 2.1 years). An episode of poor asthma control was defined as ≥1 of the following each month: (1) an absence from school attributable to respiratory illness/ asthma;(2) average use of rescue medication >2 times per week (not including preexercise treatment);or (3) >1 red or yellow peak flowmeter reading. RESULTS.Two hundred forty children completed the study. There were no differences in the likelihood of an episode of poor asthma control between the baseline period and the follow-up period for the usual-care group. For the supervised-therapy group, however, the odds of experiencing an episode of poor asthma control during the baseline period were 1.57 times the odds of experiencing an episode of poor asthma control during the follow-up period. Generalized estimating equation modeling revealed a marginally significant intervention-time period interaction, indicating that children in the supervised-therapy group showed greater improvement in asthma control. CONCLUSIONS. Supervised asthma therapy improves asthma control. Clinicians who have pediatric patients with asthma with poor outcomes that may be attributable to nonadherence should consider supervised therapy. © 2009 by the American Academy of Pediatrics.