It would be more natural: A tanár egy diákot vár.
Can you say," A tanár vár a diákra?"
"A tanár vár egy diákra" is correct.
Yes, I see your point. The "a" in "a student" requires "egy".Thank you. Köszönöm.
Would saying "A tanár egy diákért vár." also be correct?
No. Both "-ért" and "-ra/re" can be translated as "for", but "diákra" is a reason, while "diákért" is a purpose. So the reason (and not the purpose) why the teacher is waiting is a student (who is supposed to arrive).
A tanár egy diákra vár!