CK-12 Foundation
The CK-12 Foundation is a non-profit organization dedicated to increasing access to high-quality K-12 STEM education materials. All of CK-12’s content, including more than 3000 science concepts, is 100% free and is curated by experienced educators. Teachers can use the site to find and build lesson plans, pacing guides, differentiation guides, in-class presentations and more. CK-12 also offers educators access to free, standards-aligned textbooks for earth science, life science, physical science, biology, chemistry, physics and more.