One of my favorite add-ons and extensions is Doctopus and Goobric.  With Doctopus and Goobric, you import your classes into a Google Spreadsheet, create a rubric, and grade these assignments with the rubric attached.  It is an amazing and useful tool for the classroom.

In the presentation below, I have attached directions and videos to use Doctopus and Goobric in your own classroom.

If you have any questions, please let me know!