National Student Leadership Conference in Political Action & Public Policy: 

http://www.nslcleaders.org/youth-leadership-programs/political-action-public-policy/

Georgetown University--Summer at Georgetown for HS Students: http://scs.georgetown.edu/courses/1279/american-politics

Emerson University--Pre-College Programs, Political Communications Program: 

http://www.emerson.edu/academics/pre-college/pre-college-institutes/political-communication-program

JSA--Pre-College Summer School and Instiutes:  http://summer.jsa.org/programs/summer-institutes/

St. Albans School: http://www.stalbansschool.org/page.aspx?pid=413