Still around are some of us who attended high school through the years 1906-1910. In my case that was in Zanesville, Ohio, which periodically over the years has been portrayed in magazine articles as "the typical American town." In those days high school principals did not seem to be chosen primarily as administrators specially skilled in management. The principal of a school was the principal teacher, supposed to be something of a scholar, often addressed as "professor." He was expected to be familiar with the subject-matter of the curriculum as a whole. If a teacher had to be absent for a day or two, in most cases the principal could step in and temporarily take over the class.
Foley, L. (1976). Amateur Etymologists at Play. Reading Horizons, 16 (4). Retrieved from http://scholarworks.wmich.edu/reading_horizons/vol16/iss4/11