This study describes the design and implementation of an integrated STEM + computational thinking (CT) curriculum, which was guided by project-based learning, for integrating CT in after-school programs. The study examined teachers and students' reactions to the curriculum and the challenges in implementing such a curriculum. Results show that most students and teachers reacted positively toward the curriculum. Main challenges to implementing such a curriculum were also identified. Lessons learned from the curriculum implementation are discussed. The study contributes to the integration of CT and development of CT in students. It also contributes to teacher professional development regarding CT integration.