At least three school students were killed and nearly 25 others injured when a school bus fell from a bridge in Punjab's Gurdaspur district on Tuesday morning, police said.The bus, belonging to a private school, was ferrying the students to the school in Fatehgarh Churian town near Batala, 260 km from here. The injured students were taken to hospitals in Batala and Amritsar.The accident took place when a van collided with the school bus. Its driver lost control over the bus, which smashed against the railing on the small bridge and fell into a drain.