Background: Teachers' beliefs play an important role in how teachers think about how students learn, and how content should be organized and taught. Integrated STEM is pushing the boundaries of some of the traditional assumptions in education-disciplined-based courses, courses taught independently by teachers, standards and content-driven, and no collaborative planning time for teachers. Six teachers, located in two high schools, participated in a year-long program to develop interdisciplinary collaboration to implement integrated STEM learning in their courses. A qualitative instrumental case study of the two teams of teachers was conducted to gain insights and understandings of the teachers' beliefs and instructional practices of STEM integration through interdisciplinary approaches in a complex system (i.e., hydroponics). Results: Themes regarding features, beliefs and practices, and challenges emerged from cross-case analysis of the teachers' stories, which resulted in two interdisciplinary collaboration models, multi-classroom and extracurricular activity, from each of the teams at each of the two high schools. Multi-classroom and extracurricular activity models had some resemblances, but also had differences. Both cases had the same goals to use real-world problems to help students see STEM connections, learn STEM knowledge and skills, and apply STEM knowledge and skills to solve real-world problems. Conclusions: Based on teachers' beliefs and their interdisciplinary STEM collaboration practices, three components were identified. Team size, teaching goal, and collaboration structure highly affect a successful interdisciplinary STEM collaboration model in high school settings. The study also contributes to expend the concept of a continuum of STEM approaches to curriculum integration, disciplinary, multidisciplinary, interdisciplinary, and transdisciplinary (Vasquez, Sneider, & Comer, STEM lesson essentials: Integrating science, technology, engineering, and mathematics, 2013), and provides frameworks for structuring a successful interdisciplinary collaboration model in high school settings.
