Northwestern University National High School Music Institute in Evanston Illinois is June 27-June 30, 2010. This is what they need for an application (?!), it looks like a college application, plus an audition:
• Complete this information form and mail it to the address listed below.
• Write a brief history of your musical background on a separate sheet of paper. Please include information about your activities in music: length of study; private teacher(s); participation in special workshops; a list of works you have studied and performed in the last four years; solo performances; choral, jazz, orchestral, or wind ensemble experience; chamber music experience; roles in school productions; secondary instruments, etc.
• Request that your guidance counselor provide us with information on
your academic background. Please provide your counselor with a stamped envelope addressed to us and ask that the following items be sent:
• A transcript of your high school record
• Your grade point average
• Your high school class rank
• Your PSAT, SAT, and/or PLAN, ACT scores
The application fee is $50, about on par with college applications
It's five weeks for $4700 (by contrast Marrowstone Music Festival in WA is 2 weeks for about $2500)