This study examines healthcare utilization over time in Bronx, New York schoolchildren with asthma who were previously identified via parent surveys in six elementary schools. Four of the schools have on-site school-based health centers (SBHCs), and two do not have on-site health services (control schools). At baseline, we reported an asthma prevalence of 20%, and high rates of emergency department (ED) use (46%) in the previous year. To determine if asthma morbidity (specifically, ED use, community provider use, and hospitalizations for asthma) could be reduced by incorporating an aggressive intervention at two schools with SBHCs, we prospectively followed children for up to 3 years. Parents were scheduled for interviews every 6 months, and were queried about their children's use of health services for asthma in the prior 6 months. In multivariate models, children in the two intervention SBHC schools were less likely to have visited a community provider for asthma (relative rate ratio, 0.52; 95% confidence interval (CI), 0.30-0.88) or an emergency department for asthma (odds ratio, 0.44; 95% CI, 0.14-1.38; P = 0.059) in the prior 6 months compared to children attending control schools. There was no difference in community provider use or emergency department use for asthma between children attending nonintervention SBHCs and control schools. However, school type did not affect asthma hospitalization rates, which declined in all groups. Our findings support the effectiveness of aggressive school-based asthma services provided by SBHCs to reduce asthma morbidity and complement community health services.