Mark has taught, written and presented on Challenge Based Learning over a number of years.
See http://ali.apple.com/cbl for the background to CBL.
[Graphic licensed under terms & conditions [Graphic River - Envato Marketplace].
His resources on Challenge Based Learning are linked below under these blog tags.
http://ictedservices.typepad.com/icted_services/cbl/
http://ictedservices.typepad.com/elearning/challenge-based-learning/
There are also CBL video interviews here.