Catch Sick Science videos every Tuesday on YouTube. Sick Science just posted their 100th video last week on Moss Graffiti- see embedded below. The clips typically show you how to set up a science demonstration or investigation and then leave the audience with a question or prompt to respond to in the comments.
These clips seem appropriate for elementary and middle school students. With 100 videos there is a substantial set to search and use for science fair projects or to supplement a concept you are teaching.