State-controlled media said Tuesday that the girl's post used language from a famous speech by Ho Chi Minh in 1946 appealing for resistance against French colonialists.
The post joked about never having to take exams again.
Phap Luat Viet Nam quoted a local official in Quang Nam province as saying the girl had "distorted history and seriously insulted teachers."
The girl said the posting was "just for fun."
The current Communist government doesn't allow freedom of speech.