PA was measured using ActiGraph accelerometers (ActiGraph models GT1M and GT3X, Pensacola, FL). Accelerometers were initialized to save data in 15-second intervals (epochs) to account for the spontaneous PA of 4-year-old children. Children wore the accelerometers on an elastic belt on the right hip (anterior to the iliac crest) for 5 consecutive weekdays (Monday to Friday). Parents were instructed to remove the accelerometer during water activities (bathing, swimming) and when the child went to bed. Trained data collectors checked each child's accelerometer at the beginning of each school day. If a child was not wearing the accelerometer upon arrival at preschool, study staff provided a temporary accelerometer for the child to wear that day. Accelerometer data were later linked for each child. Trained data collectors recorded participants' arrival and departure times from the preschools every day, to distinguish In-School PA from Non-School PA. Each child's daily PA data were summarized by time period: In-School, Non-School, and All Day.