Here are some thoughts: 1. Instead of grading, maybe you can use it for training, tutoring. If a student is learning to write essays, I'm assuming it's hard for them to get any feedback. 2. But then there's probably not enough money to be earned there.

One trick might be to write an independent AI to summarize the essay back and see how closely it matches the essay title. This might weed out gibberish essays with sound English sentences.