Translation:I am a student, what about you?
How about "I am a pupil, what about you?". 学生 represents both, studend and pupil, doesn't it?
Duo often accepts typos if the mistake does not create an actual word. For instance, it would not be accepted if you typed hot or now instead of how, but it might accept something like gow.
For the English translation to be correct, you absolutely need the indefinite article of "a" here.