The challenge board is something that is displayed, all at once, in the front of my classroom. Students are encouraged to select any number of these to solve by a given date. Students choose to work alone on some challenges and on others they work with a partner. Most importantly the challenge board gives students the opportunity to explore within a unit what interests them. You will also notice that students always have the option to create their own challenge, with oversight from myself and a panel of fellow students.
Below is an example of a challenge board that I created for high school students to further examine Lichens as bio-indicators.