The folks at the School of Psychology at the University of Plymouth released study results that point to doodling as a way to increase retention. They took a boring recording of a list of names and locations and asked people to listen to the long list and remember which were heading to a party. Half of the study participants were asked to color in random shapes while listening, while the control group did nothing but listen to the long list of names. The result was that those who doodled while listening named, on average, 7.5 of the 8 names going to the party, while those who didn't doodle listed only 5.
While it seems a bit odd to 1.) listen to a long list of names, and 2.) be told to do something that is usually unacceptable as a matter of course, the point of the study was to illustrate how something bad can actually be good. Put another way, doodling while listening to someone drone on and on prevents the mind from slipping into daydreaming or "zoning out" by giving the mind a cognitively undemanding task to perform. It's just enough to keep the mind present.
Boring teachers take heart: If your students are doodling, they are retaining more!