We have a school-wide subscription to turnitin.com  It's the most common one that schools use around here.  I would check to see if your local high school does subscribe to it before you start exploring other options.  I don't know of any elementary schools that subscribe and there are some middle schools.  Teachers should be working on teaching students how to take notes, summarize and paraphrase ( that might be a good afterschool workshop for a public library to hold)  The software is just a writing tool and should not be used as a "gotcha".