In a class, a teacher corrects/punishes a student if he/she is wrong; but in the exam hall, he doesn't even if he/she finds the students writing incorrectly. -> We are in a exam hall now, we are free to do anything, nobody warns us; we are learned. In this exam hall, we have the almighty as the invigilator; he will evaluate the scripts and will grade us accordingly....
From my Teacher Abdul Wazed Chowdhury