Prosecutors charged all nine students with making illegal threats, with two charged additionally with causing bodily harm (vållande till kroppsskada).
The staff member, who approved the students' plan to scare the boy with the iron, faces charges of being an accessory to making illegal threats, with an alternative charge of being an accessory to assault.
The school, which is the alma mater of Prince Carl Philip, was forced to close its doors temporarily following the hazing scandal, which saw one 14-year-old boy taken to hospital due to the severity of his burns.
During the incident, the victims were told to lie on the floor and were made to believe they were about to be burnt with a hot iron. Some of them were then burned on their backs after one of the attackers said "Now this is going to hurt". The students responsible claimed they didn't intend to burn their fellow students, but they did not think to check if the iron was still warm after it had been unplugged.
Speaking with Sveriges Television (SVT) on Wednesday morning ahead of the opening of the trial, Education Minister Jan Björklund said he believed the boarding school should be responsible for the well-being of students outside the classroom.
"If you send your kids to boarding school, you expect the school's leadership to also be responsible for what happens during free time," Björklund told SVT.
In December, the Administrative Court of Appeal affirmed a lower court ruling that Sweden's School Inspectorate (Skolinspektionen) was wrong to temporarily close Lundsberg after the scandal emerged, concluding that the agency lacked supervisory authority to take action for matters that occurred outside the classroom. The hazing incident took place in the dorms.
The education minister also commented on the government inquiry into reforms at Sweden's three national boarding schools, Lundsberg, Sigtuna, and Grenna.
"Those three schools have had special standing, perks that go way back. They're going to be like regular free schools in the future," he said.
The inquiry proposes that the schools no longer be able to accept tuition for lessons, although students would still pay for room and board.