Examples from literature

• A correspondence course would be splendid for him if he can't get away from the farm for regular college work. 
• A great many of the girls and boys took correspondence courses in stenography, drawing, bookkeeping, illustrating, etc., etc. The purely mechanical work of the mill does not satisfy them. 
• He began at once with correspondence courses in mechanical and electrical engineering. 
• I am taking two correspondence courses, and mean to continue my studies here in my wagon. 
• The school also directs extension classes in outlying parts of the city and neighboring places and correspondence courses for study classes and individual students in all parts of the country.