Some recently published research by the cognitive sciences department at Princetown University indicates that disfluent material offers better learning outcomes.
Disfluency is the subjective feeling that the task seems harder than it is.
This was done in quite a simple way, two groups were given an identical set of information. One group had this presented in 100% black 16pt arial, nice and easy to read and the other group had the same content in 75% black 12pt comic sans or bodoni.
The second group showed significantly better recall of the information by 14%.
Worth thinking about when designing and presenting your modules.

This is very interesting, Nick.
Do you know by chance a source of more information?
[:)]

Hidden on the Princetown Uni phsycology web site. I'll see if I can find it again!
It's also published but unless you can access the medical libraries you'll just get an extract or synopsis.
Adam Alter (New York University Stern School ) has some nice items on fluency, that is clarity od message and gives nice pointers on how to skew reactions with quite simple changes.
The disfluency study is quite new and on the face of it seems to be counter intuitive. But kind of obvious, if you have to concentrate a little more on something then you're more likely to remember it.