一中 is short for
第一中学 — in nearly every Chinese city and county, 'the No. 1 Middle School' is the most prestigious public high school, the one whose gaokao scores parents compare. e.g.
人大附中 is informally one of
北京 top choices;
衡水一中 in Hebei is famous (and notorious) for its boot-camp exam-prep culture.
