Shimla, July. 1(HS): Four have been killed and seven injured while a school rolled down a hill in Lower Khalini area of Shimla. Police and rescue teams reached the spot. Reportedly, three school girls and driver have died in this incident. The children were from Chelsea School of Shilma. Injured children have suffered grievous head injuries.The official said that the bus conductor is also among injured. Injured persons have been admitted to the hospital. The villagers said that the road has neither railing nor any security arrangement.