I've seen students approach these presentations in two different ways. Some get in front of the room and give a lot of "I think" statements. This is a fine start, but if the project is going to be successful, they really need more substancial research to back it up. Other students, however, have made themselves into Wikipedia. They'll stand in front of the room and present tons of information (perhaps even well organized) but at the end of the day, they don't really say anything about it. I've asked many of them "and? You're the expert, right? What should we take away from this?" I think the students are so accustomed to speaking about "just the facts" in class and sticking only with their opinions the rest of the time that it's sometimes difficult to take ownership and say "yes, I can speak definitively about this. I'm an expert."
Now granted, this is tough for any high school student. In fact, this is one of the biggest hurdles that students in the Ph.D. program had to overcome: being able to speak as experts in their field. While I wouldn't say any of my students are legitimate "scholars" on their topics (that will come with time), they're well on their way, and they should feel free to start merging the gap between fact and opinion. They'll soon find that either in isolation is actually quite useless.