I think of the number of times that a student has come to my office to question his or her grade. I would ask them: "Can you read to me what you wrote? Just read it aloud to me." They would start reading, then stop and say: "Well, I didn't write xxx, but of course that was what I had in mind". They would continue, then stop in some embarrassment at the lameness of their style. The lack of precision in their writing would be painfully obvious, and sometimes they couldn't help but laugh at themselves. I wouldn't need to explain why they didn't get full credit: once they read aloud, the reasons became obvious.
A webcast might be the answer!