In June, 2010, noted author and Chronicle columnist on teaching and learning, James M. Lang, suggested that when learning seems easy, the result may be shallower learning.  This phenomenon, called cognitive disfluency, creates a challenge.  If material is too hard, learning could be shut off.  What we need to create, Lang suggested, is desirable difficulties – just enough difficulty to encourage deep learning and not shut off motivation to learn.  Lang asked participants at a teaching conference to identify strategies that characterize desirable difficulties that would safely bring about cognitive disfluency.  Here are the strategies (June 4, 2010, The Chronicle Review):

• Ask students to process or translate course material using unusual rhetorical or expressive modes. I have always listened with skepticism to accounts of teachers asking their students to translate course concepts into 140-character status updates. But my workshop participants argued that having students take concepts and rework them in the form of a text message, or a Twitter update, or even visual representations or performances, could have the same defamiliarizing effect that might be achieved by a change in fonts.
• Require students to argue on behalf of unfamiliar positions. One of my participants was a political scientist who asks her students to debate issues in the Arab-Israeli conflict—and routinely requires them to argue against their personally held convictions. Another participant, who teaches a course for medical students on abortion, does the same. In both cases, they observed, students are forced into the uncomfortable and defamiliarizing position of having to look at a well-trod debate from a new angle.
• Ask students to find or identify mistakes. A professor of architecture noted that he occasionally makes mistakes while doing calculations on the board, and that his students had learned to watch out for those errors and correct him. A math professor then pointed out that he would sometimes deliberately seed mistakes into assigned problems and ask students to find them. In both cases students were nudged out of the mode of simply observing or running through the problems on automatic pilot. That may seem like an artificial technique, or like playing games with students—but only until you stop and think about how many jobs require people to review presentations, problems, performances, or communications and make sure they are mistake-free.
• Plan for failure. A faculty member in chemistry said you can wake students up by asking them to undertake short experiments that are designed to fail. Rather than simply going through the motions of a lab, and finding the expected result planned for them by the teacher, students learn what every experienced researcher in the world knows: that experiments, like scholarly research of any kind, almost never proceed exactly as you planned them, and that you can learn a lot from your failures.