The bus driver was critically injured. None of the other injuries were serious, officials said. At least a dozen students were taken to an area hospital for treatment.
The bus rear-ended the tractor-trailer on the Pennsylvania Turnpike as the truck re-entered the travel lanes from a pull-off area before dawn in Wallace Township, about 35 miles west of Philadelphia, state Trooper Kevin Rathman said.
The truck had reached about 40 mph when it was struck by the bus, which was going about 60 mph, police said. The front of the bus was obliterated.
The bus was carrying students from Elizabeth Forward High School in the Pittsburgh suburb of Elizabeth to the Tournament of Bands Weekend in Wildwood, N.J., said Jane Milner, a school district spokeswoman.
Bus driver Timothy Berkshire, 49, was flown to Lancaster General Hospital in critical condition, hospital spokeswoman Jill Gross said. Truck driver Willie Ruff, 58, escaped injury. It wasn't known whether either driver would be cited.
A 10-mile stretch of turnpike was closed to allow emergency access to the site, including helicopters. It was fully reopened within six hours.
The bus was carrying 29 students, the band director, three other staff members and seven parents, Milner said.
The band gathering was to start Thursday night and run through Sunday. The school's officials canceled participation in the competition.
By about 10 a.m., many students were being reunited with worried parents, who had driven several hours, reports CBS radio station KYW-AM. Other students were resting and waiting for the school to send a replacement bus to bring them back home. A few expressed reservations about getting on another bus after their recent experience.
Phones at the bus company's offices were continually busy Thursday morning.