In conjunction with the thesis statement, a research paper should be inquiry-driven and purposeful. I see so many research papers that are not, and I think that even at the middle-school level, students can have a big question and a purpose.
On another note, what I have found is that when teaching students how to cite, there is far more to focus on than just plagiarism. We have a discussion in which I try to elicit the reasons for citation, for example, how people will want to find out more about the topic, how people will see that the source is good, how people deserve credit for their ideas, and so on. When we make a great dish, don't we tell people where we got the recipe? It just seems to me that there are so many positive reasons to document our sources, and no one seems to emphasize those.