This is a rubric I developed to help me assess my high school art students' artist statements. My students write a statement for almost every project, using the handout from theartofed.com to help them, and post to Artsonia. This rubric helps me to fairly assess their writing and give them feedback for improvement. I circle the level that describes their work in each category, type a number from that level into a calculator, and average the results to get their grade.
This purchase includes a version in Word and one in Pages that you can edit as needed, as well as a PDF. The grades and numbers reflect what I am required to use at my school, but you could easily change it to 1-5, "proficient, exceeds, etc", or whatever works for you and your school.