General Information on Workshops:
Thinking about taking a creative writing class? Check out these articles --

• How to be Class Conscious by Tim Waggoner
• The Write Class by Steven Piziks
• Writers' Workshops by James Patrick Kelly
• Compare summer Science Fiction & Fantasy workshops in The Family of Summer SF Workshops by Trent Walters

Speculative Fiction Writing Workshops -Teens:

• Alpha, the Science Fiction, Fantasy and Horror Workshop for Young Writers  ages 14-19 runs for ten days every July in the Pittsburgh area in conjunction with Pittsburgh's science fiction convention Confluence.

Speculative Fiction Writing Workshops - Adults:
Although these workshops are for adults, many have been successfully attended by older teens.

• Clarion  is a six week summer intensive workshop at the University of California at San Diego.
  From 1972-2006, Clarion was at Michigan State University, E. Lansing, MI.
• Clarion South in Australia
• Clarion West  similar to Clarion, is a six week summer intensive workshop in Seattle, WA.
• Odyssey  is a six week summer intensive workshop in New Hampshire.
• Oregon Coast Professional Fiction Writers Workshop
• Uncle Orson's Boot Camp  Week long writing workshop offered by Orson Scott Card in June in Virginia. Details usually appear in January or February on his website
• Viable Paradise: Fantasy & Science Fiction Writers' Workshop  on Martha's Vineyard, MA, one week in October
• Writer's Workshop  is a two week workshop at the  Center for the Study of Science Fiction at the University of Kansas

  In addition, several conventions offer short writing workshops including

• Wiscon Writers' Workshop
• Context Writing Workshops

Summer Writing Programs for Teens:

• California State Summer School of the Arts
• Centauri Summer Arts Camp
  Niagara, Canada
• Converse College Young Writers Summer Workshop
  Spartanburg, SC
• Duke Creative Writers' Workshop 
  for grades 10 & 11; Durham, North Carolina
• Duke Young Writers Camp
  for grades 6-11; Durham, North Carolina
• Interlochen Center for the Arts
• Iowa Young Writers' Studio
• Jonathan R. Reynolds Young Writers Workshop
  at Denison University; Granville, Ohio
• Kenyon Review Young Writers Workshop
  at Kenyon College, Gambier, OH
• New England Young Writers' Conference
  for students from New England and New York
• New York State Summer Young Writers Institute
• National Book Foundation's Summer Camp
• Sewanee Young Writers Conference
  Sewanee, TN
• Writers Workshop at Susquehanna University
• Thinking & Writing: Workshops
  Great Barrington, MA; Portland, OR; Lake Forest, IL
• The University of Virginia's Young Writers Workshop
  Charlottesville, VA
• Young Writers Workshop at North Carolina State University

• TeenInk lists a large number of summer program including many in writing in their classified ads section.