This is something I struggle with. In the AP classroom, I am very strict about plagiarism because these students will soon be in colleges. With my middle school students who are just learning to researc, I am a little looser My main focus with them is summarizing and citing, even if for the bulk of them it means cutting and pasting a web address. Tools like citationmachine and bibme make the issue of citing a lot easier, and as far as policing, I find it very easy to google search suspicious sentences and have usually been able to catch students in the process.
Plagiarism is using others’ ideas and words without clearly acknowledging the source of that information.
To avoid plagiarism, you must give credit whenever you use
another person’s idea, opinion, or theory;
any facts, statistics, graphs, drawings—any pieces of information—that are not common knowledge;
quotations of another person’s actual spoken or written words; or
paraphrase of another person’s spoken or written words.
These guidelines are taken from the Code of Student Rights, Responsibilities, and Conduct.