Scenario: Measures: * Actigraph accelerometer: Worn by the participant throughout the day to measure daily MVPA duration. * Observation checklist: Used by trained observers to record specific physical activities engaged in by the participant. Data Aggregation: Daily MVPA data from the accelerometer will be averaged across baseline (A) and intervention (B) phases. Visual Inspection: Line graphs will be used to visually analyze changes in MVPA duration across phases. Reliability and Validity: Inter-rater reliability for observation data. Describe the measurement system you will use in the study including the relevant dimension(s) of the dependent variable (Daily duration of MVPA measured using accelerometers at home and school.). Discuss how the data will be collected, how it will be aggregated, and the type of graph you will use to visually inspect the data. Finalize this section with a discussion of how you will evaluate the validity and reliability of the data