Curriculum based on open educational resources (OER) -- materials that are free for educators and students to use, customize, and share -- represent a small portion of all K-12 recent adoptions, at slightly over 5%. OER are concentrated in Mathematics, where 14% of adoption decisions were OER (compared to 4% for English Language Arts, 2% for Science, and 1% for History and Social Studies). Despite the small numbers, those who select OER view the overall quality as slightly better than commercial alternatives, and considerably better on multiple specific aspects of teaching and learning, such as extending the core knowledge to novel tasks and situations, and collaborating with others. The use of external curriculum review sites during the selection process is associated with higher OER adoption rates; districts that did not employ an external review site in their selection process were least likely to adopt an OER solution. This study examines curricula adoption decisions and use among K-12 schools and districts in the U.S. A total of 2,137 respondents are included in the analysis, composed of district administrators, school-level administrators, and in-class teachers. As part of the broader questions surrounding adoption decisions, the study includes a more detailed examination of OER awareness, OER adoption rates, the impact of OER on teaching and learning, and the relationship between the effectiveness of the adopted curriculum and the overall effectiveness of the professional development used to support it. The responses for this study were collected prior to the shift to emergency distance learning in schools and districts across the country spurred by COVID-19. Such a massive effort on the part of so many in the K-12 universe will no doubt impact their options, strategies, and future plans, so the results presented here need to be viewed through that lens.