Teacher prompting is a means to increase preschool children's physical activity. Twelve 4- and 5-year-olds at one preschool in the southwest U.S. participated in an ABA prompting intervention that utilized a bug-in-the-ear device to signal teachers to prompt sedentary children to increase physical activity level during unstructured recess. RM-ANOVA was used to analyze prompt rate across phases and visual analysis and Tau-U were used to analyze physical activity level (measured by accelerometry and systematic observation) across phases for the entire recess period (i.e., macro analysis). The latter methods were also used to compare accelerometer activity counts pre- and post prompt (i.e., microanalysis). Prompt rate was near zero at baseline; rose greater than 24- fold during intervention; and then dropped to near-baseline level at withdrawal. For observational data, sedentary activity and light and moderate-to-vigorous physical activity (MVPA) were statistically significantly lower and higher, respectively, during the intervention than at baseline/withdrawal. For accelerometry data, only MVPA was statistically significantly higher during the intervention than at baseline/withdrawal. Microanalysis revealed that post prompt physical activity rose and exceeded the light intensity threshold when teachers initiated prompts and rose but did not exceed the light intensity threshold under intervention prompting conditions. Prompting stimulates light physical activity immediately after sedentary activity is detected and decreases overall sedentary activity over an entire recess period.