Asthma is a chronic lung disease characterized by airway hyper-reactivity, inflammation, and obstruction. Asthma is also a leading cause of school absenteeism, and thus of concern to physical educators and health professionals. The purpose of this study was to assess aerobic performance by children with and without asthma. All participants were tested on the Progressive Aerobic Cardiovascular Endurance Run (PACER). Of particular interest was children's aerobic performance over an extended time, i.e., 15 months. Participants (Grades 4-8, N = 809) were tested on the PACER three times during the school year with two follow-up tests during the succeeding school year. Among the 809 participants were 103 children with mild-moderate asthma. Hierarchical Linear Modeling (HLM) was applied to analyze the data. Notwithstanding their lower scores at baseline (intercept), children with asthma increased their PACER scores at a rate more than double that of their peers without asthma. Although more than one PACER trial may be needed to accurately determine children's aerobic performance, repeated trials may be especially necessary for children with asthma. It was further concluded that the PACER is an effective tool with which to assess aerobic performance by middle school children with well-managed asthma.