There are numerous research reports on OERhub.net. This organization is basked in the UK and most of these reports are from an International, multi-grade level perspective.
OpenEdGroup.org This organization looks specifically at student outcomes (grades) when comparing OER to CT (commercial texts). This group conducts OER research and shares it with other researchers and stakeholders in the field. They provide you can find multiple studies and publications on their website, as well as resources for anyone wanting to conduct research.
OER Adoption Impact Calculator Helps you understand many of the potential impacts of adopting OER instead of traditionally copyrighted learning materials.
The Review Project This review provides a summary of all known empirical research on the impacts of OER adoption. The information is periodically updated with new articles as we become aware of them.
Current OER Research from the OER Research Fellows created by John Hilton III of the Open Education Group and the OER Research Fellows.
Four years and falling: Impact of statewide funding for textbook affordability An article summarizing the findings of Oregon's OER initiative over the past four years.
Openpedagogy.org How teaching and learning is different/better/more flexible with OER and open educational practice?. There is a relatively new field of study called open pedagogy that is exploring exactly these questions.
OpenEdGroup.org This organization looks specifically at student outcomes (grades) when comparing OER to CT (commercial texts).
John Hilton III. “Open Educational Resources, Student Efficacy, and User Perceptions: A Synthesis of Research Published Between 2015 and 2018.” Education Tech Research Dev, 6 August, 2019.
Virginia Clinton and Shafiq Khan. “Efficacy of Open Textbook Adoption on Learning Performance and Course Withdrawal Rates: A Meta-Analysis.” American Educational Research Association, 2019, 5 (3), 1-20.
Phillip Grimaldi, Debshila Basu Mallick, Andrew Waters, Richard Baraniuk. “Do Open Educational Resources Improve Student Learning? Implications of the Access Hypothesis.” PLOS One 14(3)
There is recent research from University of Georgia (2018) that showed Pell-eligible and “minority” students had even better outcomes than “traditional” students when enrolled in courses using OER vs. traditional textbooks. This research study was shared at an CTE OER webinar in August 2019; you can see the slides here (see slide #12-20)
Ashford, Ellie and Matthew Dembicki. "Promising but tough road for OER degree pathways". Community College Daily Feb. 2020.
Colvard, Nicholas B., C. Edward Watson and Hyojin Park. "The Impact of Open Educational Resources on Various Student Success Metrics". International Journal of Teaching and Learning, 2018
OER Impact Research Webinar Hosted November 13, 2019, this webinar shares the most current information on OER Impact Research