It is utter delusion to leave the children on their own, as far as revision is concerned, and at the end you expect good results. It happens but the chances are very thin.
Parents need to have a hand in supporting their children, through making sure home work is done, and in time. When children are motivated, which can succefully be done by their parents; they perform well in their academics.
Being torn apart between TV and home work, they need our initiative in order to focus most of their time on books.