Chamba: As many as 25 school students sustained injuries when a tractor trolley turned turtle while it was on an upward journey on Koti-Ladog link road, 32 km from here, this afternoon. District police chief Madhusudan Sharma said that about 25 students after school recess took lift in a tractor while it was on a upward journey near Koti. At 4.30 pm the trolley got detached from the engine, rolling back and tumbling down the road, which injured most of the students. Six critically injured students were rushed to Zonal Hospital at Chamba. He also said that police were investigating the matter.