While most of the energy around Open Educational Resources is in higher education, affordable and open educational resources are important to K-12 educators as well.
Curriki is a nonprofit global community that offers free K-12 learning resources for teachers, students, and parents. The resources on Curriki cover a wide range of subjects in the arts and sciences. Curriki offers over 55,000 Open Educational Resources and its 400,000 members represent nearly 200 countries.
Khan Academy (https://www.khanacademy.org/)
Not-for-profit Khan Academy is an organization dedicated to providing a “free world-class education for anyone anywhere.” Content includes interactive challenges, assessments, and video in an array of topics for kindergartners through adult learners. Create an account to practice standardized tests and keep statistics on assignments and coursework you’ve completed, noting your progress as you learn.
Lumen Learning (http://lumenlearning.com/)
Lumen is dedicated to facilitating broad, successful adoption of OER at higher education and K-12 institutions. Lumen provides training and support for faculty members to teach open courses and also publishes open courses in over 30 high-demand subjects. Lumen’s catalog of open courseware includes courses in mathematics, general education, business, and science and technology.