The purpose of study 1 was to characterize energy expenditure (EE) during academic subjects and activities during an elementary school day. Children in 2nd-4th grades (N = 33) wore the SenseWear Armband (SWA) for five school days to measure EE. Teachers' logs were compared to SWA data to extract information about EE throughout the day. Energy expenditure was also compared among grades. After controlling for body mass, grade level was not a significant predictor of average daily caloric expenditure, F(2, 17.58) = 0.29, p = 0.75, ?[superscript 2] = 0.05. When comparing activities throughout the day, relative rates of EE differed significantly, "Wilks'" F(7, 23) = 52.2, p = 0.00, ?[subscript p][superscript 2] = 0.94, with PE and recess having higher EE than academic subjects. When academic subjects were compared (math, science, language arts), relative rate of EE was also significantly different, "Wilks'" F(2, 30) = 4.31, p = 0.02, ?[subscript p][superscript 2] = 0.22. For the full sample, relative rate EE was higher in science than in language arts. The integration of web-based activity-breaks (AB) into the school day was explored in the investigation for study 2. Specifically, the impact of 3-minute, web-based AB on EE and time off-task behavior in 2nd grade children was examined. Children (N = 38) in two classes wore a SWA for EE assessment and a modified version of the Behavioral Observation System in Schools was used to assess time off-task. Children participated twice in each of 4 conditions: control (CON), non-active breaks (NAB), one active break (1AB), and two active breaks (2AB). GoNoodle videos from the "Think About It" or "KooKoo Kangaroo" channels were used for the non-active and active breaks, respectively. Percent of time off-task was assessed prior to and following each condition. The number of AB significantly predicted EE, F(2, 68.47) = 25.85, p < 0.001 during the full instructional period. The type of break (active or non-active) did not affect percent time off-task during the pre-break lesson, F(2, 163.05) = 1.23, p = 0.30, but NAB did reduce percent time off-task during the post-break lesson, F(2, 167.26) = 13.67, p < 0.001, compared to the control and NAB conditions. Intergrating web-based AB is an effective tool to increase EE and decrease time off-task in a 2nd grade classroom. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]