This isn’t Core Knowledge’s first toe in the pond of OER [open educational resources], which generally means that materials can be downloaded for free, modified, and shared, though sometimes not for commercial gain. The group was one of two tapped by New York to create a free OER curriculum in ELA that is aligned to the Common Core State Standards. The result was widely used throughout that state and by others.
Mike McShane wrote about the development of open educational resources in the Winter 2017 issue of EdNext.
— Education Next