Most of the 50 students from Kamphaeng Phet on their way to visit Nong Nuch Garden in Chon Buri suffered minor injuries when their bus flipped over on a slippery road in Ayutthaya.
Driver Chawalit Yuyuen, 46, was severely injured and taken first to Muang district hospital and then to the provincial hospital.
Police said the accident happened at 4.30am on the Bangkok-bound Asia Highway in Tambon Bor Pong.
They blamed the slippery road surface but determined from GPS records that the bus showed had been travelling at 80 kilometres per hour.
The students had departed from Ban None Yai School in Sai Ngam district, Kamphaeng Phet, at 11 pm on Wednesday.