Following a review of the literature to identify core principles of schoolwide positive behavior interventions and supports (SWPBIS), this study employed coding methods to examine teacher concerns as expressed in their responses to an open-ended probe in five middle schools. Teachers in all schools expressed concerns for their colleagues' support for implementation, Tier 2 and 3 supports, use of reinforcement and consequences, and student investment. Fewer teachers expressed concerns for prevention, structuring the environment to support positive behavior, using data to make decisions, teaching expectations, and the need to understand the function of behavior. Within and across schools, teachers expressed diverse views as they affirmed their support, expressed concerns for their colleagues' non-support, and, in fewer cases, expressed misunderstandings or beliefs in opposition to the principles of SWPBIS. Overall, tensions seemed to stem not from opposition or resistance to SWPBIS but from poor application of the SWPBIS principles in their building--by the team, the administrators, and/or colleagues. Limitations, recommendations for practice, and future research are discussed.