This mini-symposium examines two methodologies that should be recognized as pillars of longitudinal research on motor skills and physical activity. The first is hierarchical linear modeling (HLM). HLM models individual variation in growth and permits hypothesis testing of possible growth correlates. HLM also allows investigators to examine change directly using growth curves. In essence a regression equation is calculated for each participant’s intercept (baseline performance) and slope or rate of change in performance over time. The second methodology is the time-lag sequential (TLS) research design. Prevalent in developmental psychology, TLS maximizes the strengths of longitudinal and cross-sectional designs while minimizing some inherent weaknesses. TLS has the potential (especially when combined with HLM) to produce a level of developmental clarity that neither approach when used alone can provide. As an example of the convergence of these methodologies, we will highlight an investigation of the aerobic performance of children and youth with and without asthma. Participants (grades 4-8, N=809, 103 mild-moderate asthma) were tested on the Progressive Aerobic Cardiovascular Endurance Run (PACER) three times during the school year with two follow-up tests the succeeding school year. HLM was applied to analyze the data. Notwithstanding their lower scores at baseline, 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.