Background: Rates of uncontrolled asthma vary by demographics, space, and time. This article uses data on ambulance-treated asthma attacks in children to analyze these variations so that school districts can improve their asthma management interventions. Methods: Incidence rates of 1826 ambulance-treated asthma attacks for children aged 5-18 years were calculated for school zones for elementary, middle, and high schools in the Houston (Texas) Independent School District (HISD). Zones with rates in the upper quartile were identified as the highest rate zones and were compared with other school zones in the district by demographics, location, and timing of attacks. Results: The ambulance-treated asthma rate was respectively 5, 3, and 2 times greater in the highest rate school zones compared with all other school zones for those school levels. Ambulance-treated asthma attacks in the high-rate school zones occurred most at midday and in the evening and high-rate zones were often geographically contiguous. Schools in the high-rate zones had a higher percent of socioeconomically disadvantaged students and were more often without a school nurse. Conclusion: Spatial and temporal analysis of ambulance data can be valuable tools for schools to focus policy and program interventions for the students in need of improved asthma management.