When students have questions about what we are studying, I ask them to find out the information and share it the next day. For example, we were studying earthquakes and our challenge was to build an earthquake proof structure. One student asked why there is snow on top of some volcanoes even when they are active. I asked them to write the question on the board. All students have a chance to find the answer and anyone who brings the answer written even on a scrap of paper, gets a prize. I keep a box with science stickers, bookmarks, pencils, etc. Then the students share what they learned.
I also pay attention to things students are really interested in and ask them to be my co-teacher. I ask them to find out more information about that topic and share with the class through a powerpoint, a poster, pictures, etc. I give them a week to gather the information and they share it at the beginning of class for about 3 - 5 minutes. Once students start to see their peers "teaching" then they ask to do the same. It's never happened that the entire class wants to do this. Some want to create a poster but not speak and so we hang those up so people can see their research. It is not graded.