I teach high school here at a private school. (SPOK) I teach history in high school. (SPOK) I teach religion in high school. (SPOK) with school as modifier (11 hits) The possible construction is no preposition + zero article. I teach high school English. (SPOK (1 time), FIC (4 times)) I teach high/middle school students. (SPOK (2 times), MAG (1 ... More @Wikipedia
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