THE INSTRUCTOR PILOT WAS SUPERVISING THE STUDENT PILOT IN THE CONDUCT OF A SINGLE-ENGINE APPROACH AND LANDING. THE NIGHT APPROACH WAS CONTINUED TO A SHORT FINAL. THE INSTRUCTOR ASSUMED CONTROL OF THE AIRPLANE, DUE TO OVER-CONTROLLING ON THE PART OF THE STUDENT PILOT. HE INITIATED A GO-AROUND, REQUESTING THAT THE STUDENT PILOT ADVANCE THE THROTTLES. HE DID NOT VERIFY THAT THE THROTTLES HAD BEEN ADVANCED. CONTROL OF THE AIRPLANE WAS LOST, WHEN VMC WAS NOT MAINTAINED.