Background/Purpose—Physical educators and allied health professionals are in the midst of a nationwide effort to increase youth fitness. Among several parameters central to physical fitness, none stands out more than aerobic capacity. And because aerobic capacity represents the functional limits of the O2 delivery chain, its status is a key indicator of cardiovascular health. The centerpiece of most school based physical fitness programs is effective assessment. Field based graded exercise tests such as the Progressive Aerobic Cardiovascular Endurance Run (PACER) provide valid and reliable measures of children's aerobic performance. However, questions arise as to the appropriateness of such tools for children with health impairments such as asthma. The purpose of this study was to examine aerobic performance by children grades 4-8 with and without asthma. Method—The design of this study was multi-cohort, sequential. Five cohorts of children (i.e., grades 4-8) were tested three times (September, January, May) on the PACER during the 2007-2008 school year, with follow up tests the succeeding year in September and December. Among 826 participants were 103 children with managed asthma. Analysis/Results—Hierarchical Linear Modeling (HLM) was applied to analyze the data. HLM models individual variation in growth (i.e., change) and permits hypothesis testing of possible growth correlates. Essentially a regression equation was computed for each child's baseline (intercept) and change over time (slope). Several key findings emerged: As anticipated, children with asthma performed nearly 3 fewer laps at intercept then their peers without asthma (γ = -2.74, t (804) = - 2.783, p=.006). Results for slope were reversed. Among children without asthma, PACER scores increased .19 laps/month or a gain of 2.3 laps (γ = .193, t (805)=4.217, p<.001). However, children with asthma increased their PACER scores by .424 laps/month (γ = .424, t (805)=2.272, p=. 023). In addition, PACER scores for all participants were negatively associated with BMI (p<. 001) and positively associated with after school sports participation (p<.001). Conclusions—Notwithstanding lower scores at baseline (intercept), children with asthma increased their performance on the PACER at a rate more than double that of their peers without asthma. By month 14, performances of both groups were about equal. It was tentatively concluded that the PACER is an appropriate tool with which to examine aerobic performance by children with managed asthma. It also appears that the PACER may have value as an instructional as well as an assessment tool. Keyword(s): adapted physical activity, assessment, exercise/fitness/physical activity