P21 Permission
via email
Good morning Richard, 

Thank you for your email. P21 materials and educator resources are free for educational purposes. We are happy to know you have found the P21 Common Core toolkit useful. We are happy to grant you permission to use P21 materials, as long as no P21 materials and references are used to imply P21 endorsement. You will not need to seek permission again to use our resources as you build your site. Please do cite and link to our website

And again for your reference you can see our full terms of use here: 

Let me know if you have any other questions,

Lizzette Arias