This thread seems to have been resurrected. My Masters Dissertation was based on the use of Moodle to improve assessment for learning.
Black and Wiliam (note the spelling only one L) did some work in the UK which may be of interest to people reading this thread.
http://weaeducation.typepad.co.uk/files/blackbox-1.pdf
http://www.nuffieldfoundation.org/sites/default/files/files/beyond_blackbox.pdf
I hope these links are useful.
Cheers
Dave