"A large percentage of that time is then spent marking up grammar and spelling."

As an aside, I don't think this is the optimal way to teach people how to write. What were the ideas in those papers? How were they organized? Do the student's arguments make sense? I think that's what most students spend most of their time thinking about when writing an essay, and it can be a bit demoralizing to see the teacher care just as much about whether the grammar was right. Most students can fix grammar mistakes relatively easily once they notice them anyway.