The increased push for teaching computer science (CS) in schools in the United States requires training a large number of new K-12 teachers. The current efforts to increase the number of CS teachers have predominantly focused on training teachers from other content areas. In order to support these beginning CS teachers, we need to better understand their experiences and challenges encountered in the classroom. This study investigated U.S. CS teachers' perspectives on the demands of teaching computer science and support needed to ensure quality teaching. Results suggested that teachers face a number of challenges, including isolation, lack of adequate computer science background, and limited professional development resources.