A list of existing high school writing centers, alphabetical by state:

California
826 Valencia, San Francisco, CA

Florida
Berkeley Preparatory School, Center for Writing, Tampa, FL
Lake Highland Prepatory School, Rossman Writing Center, Orlando, FL
University HS, The Reading Writing Center, Orlando, FL

Illinois
Glenbrook North HS, The Write Place, Northbrook, IL

New York
North Shore HS Writing Center, Sea Cliff, NY

Pennsylvania
Mercersburg Academy Writing Center, Mercersburg, PA

Tennessee
The McCallie School, Caldwell Writing Center, Chattanooga, TN

Washington
Kentridge HS Student Writing Center, Kent, WA

Wisconsin
Kettle Morain HS, The Write Place, Wales, WI
Wauwatosa East HS, Write on Time, Wauwatosa, WI