13th year programs are available in many of the countries. This is for students who may have graduated from HS, but feel they need a break before entering college. The greatest challenge is to be able to adjust to another culture and language. Another challenge is to stretch oneself to become independent, foward thinking, practice tolerance and share outside one's own family, school and community. Year long stays are recommended highly.
Students get the most for their money here.
Semester and summer stays are available for those who can not commit for longer. An example of this is the AFS Intercultural Programs. They have been hosting and sending students for over 50 years. You pay only shipping and handling. It's the place for teens to explore colleges, careers, and themselves.