We conducted a multi-year study of specialization in elementary mathematics and/or science, using data drawn from a local sample of teachers and a nationwide sample of principals. Using the theory of planned behavior, we compare and contrast teacher and principal views and decision-making processes related to elementary content specialization (ECS). Survey data indicate that specialist models were conceived as a way to better meet students' academic needs while relieving some of the rigorous demands placed on elementary teachers in the context of new content standards. In contrast, self-contained classrooms were retained in elementary schools largely due to beliefs that these traditional structures provide the best social and emotional stability for students. After presentation of survey findings, we use three local case studies to present ECS at different stages of maturity (from newly enacted to well-established), with corresponding discussion of benefits, challenges, and lessons learned. Our case study data indicate that, while newly adopted ECS models tended to face the most challenges, there may still be critical model-specific concerns at play even when specialization has been ongoing for decades. Our findings have implications for teachers and principals, as well as researchers and professional development providers.