So, I've just used this grading rubric that I designed to grade my first round of narrative essays and I'm happy to report that it is working quite well. So far, I've just been circling the sentences that best define the essay and then using that to score each section. I've been able to grade 500 word essays in about 5-6 minutes/essay, including some helpful comments at the bottom for the student on how to improve.
I think it will also cut down on grade challenges because it's pretty black and white. The student either made 1-2 grammar errors or 6-8. They either had a strong thesis statement, or a weak one.
I realize now that I should have modified it slightly for a narrative essay, which has some different elements than a standard academic essay, but it still worked out pretty well. Next year!