I'd say high school was still 3rd house. The student would still be living at home under parent's roof and control. It is at the 9th that they go away from home and do higher education.
here is some corroboration:
http://www.astrotheme.com/astrology_houses.php
The 3rd house: immediate surroundings, siblings, short trips, and studies.
It deals with communication, the close environment (siblings, colleagues, schoolmates),
primary and secondary education, apprenticeship. It also describes short trips, transportation, modern means of communication and all practical things. The third astrological house is in analogy to the third sign of the zodiac, Gemini.
The 9th house: travels, abstract and higher concepts, spirituality, and foreign matters.
It is the realm of spirituality and philosophy, higher ideals, faraway travels, both physical and inner ones.
Contrarily to the 3rd house, this house represents higher education and universities, as well as the understanding of abstract topics. It is also related to law and legality, and religion. The ninth astrological house is in analogy to the ninth sign of the zodiac, Sagittarius.