University of Maryland has a tool at Dustball.com which is supposed to check to see that research papers are original. (http://www.dustball.com/cs/plagiarism.checker/) only trouble is, it doesn’t even detect papers which are published as free term papers on SchoolSucks.com.
A quick google for a few particularly insightful phrases works pretty well for checking to see if a student stole a paper, or copied a website.
If your 6th grader all of a sudden uses the phrase “and could therefore never represent a translation” you can do a quick google and find out that they didn’t write all of that paper on Face recognition, instead they were borrowing from the entry on Affine Transformations on Wikipedia.
Yes it is possible the student is a genius and Wikipedia borrowed text from them, or they wrote the article on Wiki. I have had that happen to me a few times. But most 6th graders don’t know much about Affine Systems, so that is a bit unlikely.