FWIW, I think Duke and Cornell move on.
If you really must know how the randomization occurs (prepare for the amazing), here's the process:
1. Copy the list of law schools from lsac.org, paste into a spreadsheet, remove all city/state/application fee info, sort by alphabetical order.
2. Visit this website (first one that came up in a Google search for random number generators or some such *&^% that I thought was worth a damn): http://www.mathgoodies.com/calculators/random_no_custom.html
Plug in the ranges, hit enter, take the corresponding number and match it to the entry number in the spreadsheet, paste the corresponding law school into a group. Occasionally break the unassigned group down to the current ranges so I don't have to deal with a million repeats (you know, the number 23 coming up 5 times after it has already been picked).
3. Start a poll. After the results are in, sort it back out based on the prescribed number of schools from each group to survive. Lather, rinse, repeat.
This really is about as random as it can get.