Aren't I? Vs. Am I not? Vs. amn’t I?

“Aren’t I?” is used in informal language.

“Am I not?” is grammatical. It is formal.

Incorrect: I’m a student, aren’t I?

Correct: I’m a student, am I not?

“I am a student, aren’t I?” is accepted correct in spoken and informal written English.

“I am a student, am I not?” is correct in a formal context.

“I am a student, amn’t I?” is incorrect. However it is accepted correct in places like Scotland.