Objective: To solicit school principals' and teachers' perspectives on children's screen-related sedentary behaviour and to identify possible solutions to reduce sedentary behaviours among school-aged children. Method: In-person interviews using a semi-structured interview guide were conducted with school principals and grades five and six classroom teachers in 14 randomly selected elementary schools in London and Middlesex County, Ontario. Fourteen principals and 39 classroom teachers participated in the study. Inductive content analysis was performed independently by two researchers. Results: Both principals and teachers were very concerned about children's excessive screen viewing activities, but they did not perceive that they could play a key role in reducing these behaviours. Key barriers were identified to reducing screen-related sedentary behaviour and to children's active living both at and away from school. They included competing demands from other subjects, limited gym resources/space within the school, a lack of control over the home environment, and a perception that parents were poor role models. Notwithstanding the above barriers, principals and teachers still recommended increasing children's daily physical activity both within and outside of school hours. Furthermore, they stressed the need for parents to play a key role in reducing their children's screen-related sedentary behaviours and increasing their level of physical activity. Conclusion: School principals and teachers were very concerned about excessive screen-related behaviour among school-aged children when away from school and suggested that interventions should emphasize increasing daily physical education, promoting recreational sports at or away from school, and engaging parents in regulating screen time at home. (Contains 1 note and 3 tables.)