Background/Context: Previous work on the use of open educational resources in K-12 classrooms has generally focused on issues related to cost. The current study takes a more expansive view of openness that also accounts for adaptation and sharing in authentic classroom contexts. Purpose/Objective/Research Question/Focus of Study The study seeks to understand what a group of practicing teachers who have been introduced to an expansive vision of openness in practice perceive to be its major potentials and barriers. Setting: This study took place in two settings: 1) a series of structured summer open education institutes and 2) teachers' authentic classroom contexts 6 months after the institutes. Population/Participants/Subjects A group of practicing K-12 elementary and secondary teachers (n = 101) self-selected to participate in the institutes and the study. Intervention/Program/Practice: Institutes were focused, 3-day events wherein teachers constructed PLCs for learning about open education and applying their understanding toward creating open educational resources for their classrooms. Research Design: This mixed methods study consisted of phenomenological methods for collecting and analyzing qualitative data from a large group and survey analysis and inferential statistics for clarifying results and determining unification of voice among participants. Data Collection and Analysis: Data collection consisted of a series of large focus group/incubator sessions, an evaluative survey, and a follow-up survey. Items for the follow-up survey were constructed out of emergent themes from the focus group/incubator sessions. Findings/Results: Results revealed that participants uniformly believed that openness offers pedagogical, economic, and professional potentials for practice, but that major barriers to diffusion exist at the macro and local levels due to the political and economic realities of the teaching profession. Conclusions/Recommendations: Openness in practice has great promise for K-12 teaching and learning, but educators, researchers, and legislators should reexamine the meaning of open in educational practice to consider its benefits beyond cost and advocate for those practices that lead to greater freedom and professionalization of teaching.