Open Education Resources
AIAA encourages the use of Open Education Resources for its members
WHAT ARE OPEN EDUCATIONAL RESOURCES (OER)?
Open Educational Resources (OER) are teaching and learning materials that you may freely use and reuse, without charge. That means they have been authored or created by an individual or organization that chooses to retain few, if any, ownership rights. For some of these resources, that means you can download the resource and share it with colleagues and students. For others, it may be that you can download a resource, edit it in some way, and then re-post it as a remixed work. OER often have a Creative Commons or GNU license that state specifically how the material may be used, reused, adapted, and shared. OER Commons
Game Changer: Open Education is Changing the Rules. ISKME

OER Commons has many cost and copyright-free K-12 resources available, especially for remote learning and aligned with Common Core.
For K-12 Common Core Resources from OER Commons click here
For K-12 Remote Learning Resources from OER Commons click here
How to Search OER Commons by openauthor