School-based asthma interventions delivered by nonschool staff have been successful but are limited in their reach because of the cost and effort of bringing in outside educators and their inability to establish improved communication about asthma between schools, families, and primary care providers (PCPs). To address these problems, Columbia University and the New York City Department of Education and the New York City Department of Health and Mental Hygiene undertook a randomized controlled trial to test the efficacy of a comprehensive school-based asthma program. In this intervention, school nurses were trained to facilitate the establishment of a preventive network of care for children with asthma by coordinating communications and fostering relationships between families, PCPs, and school personnel. PCPs also received training regarding asthma management. There was limited support for this model. While case detection helped nurses identify additional students with asthma and nurses increased the amount of time spent on asthma-related tasks, PCPs did not change their medical management of asthma. Few improvements in health outcomes were achieved. Relative to controls, 12-months posttest intervention students had a reduction in activity limitations due to asthma (-35% vs -9%, p less than 0.05) and days with symptoms (26% vs 39%, p = 0.06). The intervention had no impact on the use of urgent health care services, school attendance, or caregiver's quality of life. There were also no improvements at 24-months postintervention. We faced many challenges related to case detection, training, and implementing preventive care activities, which may have hindered our success. We present these challenges, describe how we coped with them, and discuss the lessons we learned.