This study examines physical and sedentary activities of early adolescent boys and girls using Ecological Momentary Assessment (EMA), a method that can link mood and behaviors in specific social situations. Twenty-seven assessments were collected across 7 days from 82 participating adolescents, three times in seventh grade and one time in eighth grade. Assessments were completed during nonschool hours when youth had "free time." Gender differences, longitudinal trends, and associations of physical activities (PA) and small screen recreation (SSR) with moods and peer presence are examined. Boys were engaged in PA more than girls. Patterns of PA differed by gender; boys significantly decreased PA from seventh to eighth grade, whereas girls had increased PA only during the spring. PA was associated with happier mood and was more likely to occur in the presence of peers. SSR significantly increased from seventh grade to eighth grade for both boys and girls. SSR occurred more when youth were alone and was not associated with mood. Neither PA nor SSR was more likely to occur during weekdays or weekends. Implications for intervention efforts to increase PA in youth are discussed.