I understand the argument that meaningful content and student choice can facilitate both rigor and engagement (fun), but lets be real, not theoretical. I teach middle school and the main way I get students engaged is when activities are fun, but not everything can be fun. Fun doesn't always work with some of the rigorous skills and difficult content of my curriculum. However, too much rigor will burnout the kids and they won't buy-in to the class or the content. On the other hand, too much fun won't accomplish enough and will set a bad precedent when I try to introduce rigorous material.
Rigidity and rigor only go so far, especially with underprivileged students who have very little to lose. If there is no one at home checking grades, fielding calls from the school, and enforcing punishment at home, stern efforts are only going to push these student farther from an education they already undervalue. Besides, my students will forget 90% of the content they learn in my class--its much more important that they enjoy learning and coming to school. Therefore, I think we need to error on the side of fun learning.