This study aims to identify effective teaching strategies and challenges in computer science (CS) teaching and K-12 CS teachers' needs for professional development (PD). The data were collected through semi-structured interviews with five K-12 CS teachers and eight CS instructors in higher education and analyzed using thematic analysis. The findings indicated that (1) connecting the classroom to the real world, project-based assessment, and teamwork are effective teaching strategies; (2) teaching challenges include CS teachers' knowledge gaps, students' technology access and use, and elective courses; and (3) teachers' PD opportunities and needs include content and pedagogical knowledge and an ongoing learning community. The findings offer implications for K-12 CS education and teachers' PD.