Changes in patterns of physical activity are common across adolescence and are often associated with psychological factors such as feelings of athletic competence (Agans et al., 2017; Dawes et al., 2014). However, although physical activity preferences and beliefs about competence and abilities are important contributors to participation (Sallis et al., 2000), these factors are rarely studied over shorter time scales or in the context of specific recreational environments. We therefore assessed the extent to which summer camp experiences may contribute to changes in youth physical activity behavior and attitudes, and examined factors associated with these changes. Data were collected from 309 youth (85% white, 44% female, average age of 11.6) attending three different summer camps in the northeastern United States. Camper survey data were analyzed using multilevel regression models to account for potential camp-level differences in physical activity experiences. Our findings suggest that youth experiences with physical activity at camp are not isolated from prior physical activity behaviors and attitudes, but that even one-week camp sessions can lead to changes for some youth. Specifically, overall physical activity levels increased from pre-camp to the end of camp, but camper demographics and pre-camp physical activity behaviors and beliefs were associated with participants’ self-reported activity levels, self-perceived athletic competence, and eagerness for physical activity at the end of a week of camp. We also found that many campers reported decreases in their enjoyment of physical activities with which they had prior experience, and this was especially true for teens with the lowest levels of physical activity at camp. Finally, we found that youth who tried more new types of physical activity at camp reported decreased self-perceived competence but were more likely to have higher levels of physical activity while at camp. These results suggest that summer camps can enable youth to increase their physical activity levels and change their physical activity-related beliefs, but that recreational camp programs do not affect all youth similarly. Camp staff should therefore be attentive to campers’ prior experiences, and seek to tailor their programs to better support the physical activity behaviors and attitudes of all campers.