The unrest started at around 9.30 p.m. on Saturday when a group of young people crashed a party at the Rågsved school. Police were keeping watch outside the building, and between 20 and 30 people were involved in the turmoil that followed.
Four of the 11 who were arrested and detained are over 18 years old. The 11 are suspected of arson, vandalism, violent rioting and attempted severe assault.
"They are still being questioned," police spokeswoman Kia Samrell told news agency TT on Sunday afternoon.
Explaining what happened on Saturday night, police spokeswoman Elisabeth Wernsten told Swedish Radio News: “A witness saw a large gathering of younger individuals who marched towards the centre of Rågsved, where the school is. The witness suspected that the youths were going to smash the school up.”
“One person in the gang carried a baseball bat. When the police gathered to confront them, they started throwing stones and firebombs,” Wernsten said. The situation was under control by around 1 a.m.
Another police spokesowoman, Eva Nilsson, said that the incident appears to have been premeditated.
On Sunday morning, police still had no explanation as to why they had been attacked.
“This gang simply decided to get together to commit crime. There is no good reason for wanting to attack the police in this way. Nothing provoked the incident,” said Wernsten.
Police said more arrests could follow and that officers would be present in Rågsved on Sunday to keep watch and answer questions from the public.
The Rågsved school is one of the poorest performing schools in the country, with the third lowest average grade results in Sweden, according to a recent survey, which also showed that just 29 percent of pupils received high enough grades to be admitted to senior high school.