Superintendent of Police Gautam Bora said the school principal was arrested from Tinsukia civil hospital where she was undergoing medical treatment.
She was produced before the judicial magistrate's court which has sent her to judicial custody.
On the basis of the statements of the deceased girl's fellow students, it was established that the principal had reprimanded and beaten up the girl before she committed suicide on the same day, Bora said.
In her 'suicide note', the girl said the principal "slapped me before all my friends", her father Putul Sarmah said.
However, some parents of her classmates claimed the deceased girl had written on her desk some "objectionable" words about a lady teacher following which she was punished by the principal.
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