The K12 OnLine School has added a new plagiarism checker. It is called Turnitin (turn-it-in) and works when your student/child/teenager turns in his paper to the dropbox for grading. It takes awhile to thoroughly check your paper but when it's done it shows the results-- any text that is found common to other books, papers, etc. is noted and color-coded and then the paper is given a percentage as to how much is same wording. Of course for a research paper you will find that it marks quoted passages and even official titles of organizations, but that is easy to wave through. Your student can then make changes as necessary and re-submit.
My son's paper was written well, and I ran it through my subscription to Copyscape which I got for my own writing--just to make sure I have not accidentally plagiarized (premium account is only five cents per search.)
His writing was so good, I wanted to make sure it was original. It was. And it went through the Turnitin with flying "green" colors as well. It showed only 4% same text -- which were quotes and titles.
So, good work. On K12's part and on my son's part.