The electricity is wasted in more amount. when the students go out of the class the class captain should look after this things . when the students do it often the class teacher should tell the cause of wasting electricity. 
I would like to tell them what would happen to them if the leave the fans and lights on for much time and tell them all the consequences because of the on lights and fans. I would first request them all to follow up the rules like off the fans and light switches when not in use or not in need so that we can save the electricity. if they don't listen to me when I request them, then I would like to take the help of the teacher and let them follow the rules like offing the fans and the lights when not in use.
hope so my answer is useful and mark as best if possible ....^_^