Background: Collaboration has commonly been integrated in computational thinking education to foster novice learning. While the majority of existing studies on developing students' CT skills have been based on competency or personality factors, social factors have been largely ignored. Objectives: This systematic review, framed by social cognitive learning theories, aims to unravel the influencing factors of collaboration in developing computational thinking skills in K-12 education. Methods: We searched four databases and located 79 publications for synthesis analysis to identify 10 social cognitive factors from personal and learning environmental perspectives. Personal factors are gender, prior knowledge, and motivational attitudes, while the learning environmental factors are roles, partnership, interaction, culture, tools, tasks, and scaffolding. Results and Conclusions: We examined the following five major issues: (a) collaboration elements designed in learning activities; (b) social cognitive factors that might influence the development of computational thinking; (c) the influences caused by social cognitive factors; (d) students' perceived benefits of collaboration; (e) major challenges of integrating collaboration in computational thinking education. The most reported challenges in collaborative classrooms are students' misunderstanding of computational thinking knowledge, negative sentiments, and communication problems. Accordingly, a design framework to facilitate collaborative learning activities was proposed. The design framework can provide a more focused research avenue for examining the effects of collaboration in the development of computational thinking in K-12 education.