"The 26th Annual Edition of The National Dean's List, 2003-2004 honors over 179,000 high-achieving students, representing 2,500 colleges and universities throughout the country."
A five second google search shows that it's relatively distinct. The average comes out to be 72 students/school. Realistically, the numbers are probably such that the big state schools and ivy leagues have 300 each, and small colleges 15-30.
If you have a B+ in any major, they probably take you.