To add to Dan's research, here's some info on the writing center at Sonoma State University in California. http://www.sonoma.edu/programs/writingcenter/default.html
The writing center is located in the information commons on the first floor of the library. The library's circulation and reference desk are on the second floor. The writing center started in 1997 in the library. In 2000, Sonoma built a brand new library and the writing center was on the second floor there. In 2003, they moved to the information commons on the first floor.
The staff work one-on-one with students or in small groups to help them develop writing skills and also offer help to faculty on developing writing instruction. They help students recognize how to build an argument in their papers, teach proper style, and
understand their audience.
The writing center is open Monday, Wednesday, and Friday, 9:00 am to 5:00 pm, and
Tuesday and Thursday, 9:00 am to 7:00 pm. Appointments are not required at the writing center, although they do suggest it as the center is a busy place.
They offer handouts on grammar and syntax; punctuation; process issues and writing strategies; and real world tips (including resume writing). Their website provides links to dictionary and thesauri; grammar, online handbooks and style manuals; other university writing centers; and internet search engines.
Sonoma has initiated The Written English Proficiency Test (WEPT), which is test designed by Sonoma State University that all students must pass in order to graduate. "The two-hour test asks students to write a persuasive article, essay, or letter on a topic of general interest and is scored on the basis of organization, appropriateness of content, clarity and facility of expression, and mechanics." The writing center serves as the WEPT administrative office and provides workshops to help students prepare for the test.