ABSTRACT Background: Quality physical education (PE) lessons tap on the four focal areas: curriculum, instruction, policies and environment (National Association for Sport and Physical Education 2013. Quality Physical Education NASPE Resource Brief. Reston, VA: American Alliance for Health, Physical Education, Recreation and Dance). One of the approaches to enhance the quality of PE is to use digital technologies, such as the iPad and mobile applications (apps), in the classes to facilitate teachers’ instruction and students’ learning process. Although literature discussing strategies and different types of apps employed in PE classes is available, studies investigating their effectiveness on students’ physical activity (PA) level and their PA-related beliefs are scarce. The national guidelines state that students meet the recommended moderate-to-vigorous PA (MVPA) levels in PE, as children are not sufficiently active in PE classes. Recently, more PE teachers are integrating apps in their classes and, therefore, it is essential to examine whether app-integrated PE is effective in promoting children’s PA and PA-related psychosocial beliefs such as enjoyment and self-efficacy. Purpose: The study examined the short-term (two-week) effects of mobile app-integrated PE classes on children’s PA and their psychosocial beliefs. Methods: A total of 157 fourth and fifth grade children from two elementary schools in the Midwestern U.S. participated in this study in 2016. Four PE classes from one school (n = 77) served as the app-integrated group, while three classes from the comparison school (n = 80) participated as the traditional PE group. Three PE sessions were measured for both schools at baseline and post-test to examine children’s differences in PA levels and psychosocial beliefs. In the app-integrated lessons, teachers used the iPad and mobile apps to instruct during the post-test sessions. Children’s percentages of time spent in sedentary behavior, light PA, and MVPA during PE classes were measured via ActiGraph GTX3+ accelerometers. A battery of validated questionnaires were used to assess the children’s PA-related psychosocial beliefs (i.e. self-efficacy, outcome expectancy, social support, and enjoyment) in PE. Results: The changes in children’s PA were significantly different between the app-integrated and comparison groups in sedentary behavior (F (1,154) = 110.6, p < 0.001, η 2 = 0.42), light PA (F (1,154) = 97.7, p < 0.01, η 2 = 0.39), and MVPA (F (1,154) = 31.4, p < .01, η 2 = 0.17). Children in both groups demonstrated a decrease in their MVPA; however, the decrease in the app-integrated group was significantly greater than that of the comparison group (−1.6%). There were no significant differences in changes of all beliefs between the two groups. Conclusions: The short-term (two-week) app-integrated PE classes was ineffective in reducing children’s sedentary behavior and improving light PA, MVPA, and PA-related beliefs. Teachers are recommended to align the use of iPad and apps with the PE learning goals: selection of apps and pedagogy of app use need to be carefully thought out to prevent compromising children’s PA for the sake of efficient management or emphasis on other learning domains.