Today I attended a presentation at school about a system that detects plagiarism. It was quite impressive. Submit a paper, and it finds sources on the web that match sections of the paper. It's something like a world-wide Google search for all segments of the paper. It even identifies excerpts in which synonyms were substituted or sentences added.
Of course, given such a system, students will run their plagiarized papers through it or a competing service to make sure that they won't be caught. This amounts to an arms race in cheating detection and evasion. That's certainly not the point of education. We shouldn't be spending so much time and energy on the mechanics of grading and on figuring out how to game the grading system and how to construct a grading system that is resistant to gaming.
The only real way to tell whether someone knows something is to talk to the person, as I do in all my classes. Submitting something is only the first step. The second step is explaining it in person.
So ironically, perhaps one of the positive consequences of automated teaching and grading tools is to encourage more direct person-to-person contact between teachers and students.