A "bioblitz" is a 24-hour species inventory-- like a treasure hunt where you find as many species as you can. It's a great way to get kids interested in biodiversity and wildlife in general.
The biggest bioblitz is the annual National Geographic Society/ National Park Service BioBlitz, which this year is being held in Saguaro National Park, in Tucson, Arizona. I'm there right now, and I'll be posting videos that I hope you can use with your students.
The first is a kick off video, explaining what the BioBlitz is all about.