Language 

Concordia Language Villages

multiple locations. Offers immersion language programs for high school students in more than 10 languages, including Russian, Japanese, French, Swedish, and Spanish. http://www.concordialanguagevillages.org/newsite/

Languages Abroad 

offers summer language programs and camps for teenagers ages 13 and up in 50 countries and in 30 languages.

http://www.languagesabroad.com/

Middlebury-Monterey Language Academy.

Four week language immersion program. Participants must sign "No English Spoken Here" agreement. Courses are offered on four campuses: Green Mountain College in Vermont, Swarthmore College in Pennsylvania, Oberlin in Ohio, and Pomona College in California. http://mmla.middlebury.edu/about/

StudyAbroadInternational

Summer language camps for students learning French, Spanish, and English. http://www.studyabroadinternational.com/study_abroad_programs_for_Teen_Students_and_Kids.html

St. Johnsbury Academy Summer ESL Program

Email : admissions@stacademy.org

http://www.stjohnsburyacademy.org/page.cfm?p=303

TASIS (The American School in England)

English Language Program for age 11-18.

Email : usadmissions@tasis.com

http://summer.tasis.com/

Transitions Abroad 

has links to dozens of study abroad programs in language learning for high school students. http://www.transitionsabroad.com/listings/study/teen/teen_high_school_language_programs.shtml