correspondence school

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A school that offers instruction by mail, sending lessons and examinations to a student.

from the GNU version of the Collaborative International Dictionary of English.

• A school that teaches by correspondence, the instruction being based on printed instruction sheets and the recitation papers written by the student in answer to the questions or requirements of these sheets. In the broadest sense of the term correspondence school may be used to include any educational institution or department for instruction by correspondence, as in a university or other educational bodies, but the term is commonly applied to various educational institutions organized on a commercial basis, some of which offer a large variety of courses in general and technical subjects, conducted by specialists.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a school that teaches nonresident students by mail