Given the short- and long-term health implications associated with overweight and obesity plus the likelihood of overweight or obesity to continue into adulthood, addressing the causes of overweight and obesity in childhood is a significant public health concern. One underlying cause of overweight and obesity is insufficient physical activity. The Department of Health and Aging recommends children engage in at least 60 minutes of moderate to vigorous physical activity (MVPA) per day; however, these recommendations are met less frequently with increasing age, and girls less often meet these recommendations than boys. School lunch times have been identified as an ideal time for maximizing children’s physical activity (PA), but studies have shown variable levels of PA among children during this time and research indicates that during school lunch times, girls are consistently less active than boys. Understanding influences on girls’ participation in PA during this time may help to increase levels of PA for this demographic. Two South Australian schools, one government and one independent, were included in the sample. Four focus groups (three or four participants per group: total 13 participants) focusing on girls’ perceptions of PA during the lunch break were conducted. Transcripts and field notes were analyzed using a social constructionist framework and thematic content analysis. The expectation to participate in activities considered “gender appropriate”, maturation, and bullying/teasing were identified as explicit barriers to participation in lunch time play. Other important barriers included a “girls’” school uniform and feelings of inadequate competency. The ability to renegotiate gender stereotypes, a unisex school uniform, and perceived high competency were important facilitators of lunch time PA. Low levels of lunch time PA evident in many young adolescent girls may be due to many complex social factors. Therefore, these barriers may need to be addressed before any environmental interventions are likely to be effective.