The man was also given an indefinite ban on working as a teacher or participating in any children or youth activities.
The man was acquitted on two points, but convicted on the remaining 223 points in the indictment. In all there were 108 victims - most of them girls from the ages of nine to 15.
Most of the incidents dealt with abuse perpetrated through online chats, where the man convinced girls as young as nine to commit sometimes severe sexual acts.
In addition to the jail sentence, the 50-year-old man was ordered to pay 102 victims compensation ranging between 15,000 and 250,000 kroner.
The man's abuse was not constricted to online channels. He also committed physical assaults against three girls in their teens.
“The defendant has exposed a large number of children to degrading sexual experiences. Many of those affected have suffered significant psychological damage that has hampered their quality of life greatly,” the court's judgement read.
The case is thought to be one of the most comprehensive assault cases to ever ben handled by a Norwegian court.
“The number of victims is unusually high and is in itself a clear aggravating factor. The young age of the victims was also significant for sentencing,” the court wrote.
The court wrote that the former teacher went to great lengths to carry out his attacks, using a number of different profiles in chat groups where he met the children. He pretended to be both a boy and girl and struck up relationships by talking about issues relevant for kids before turning the conversations to themes with coarse sexual content.
“After trust was established, the defendant exploited kids in a manipulative, ruthless and utterly boundless way without being detected. Chat logs show that the defendant at times displayed intense and aggressive behaviour,” Judge Lars Marcus Evensen wrote in a 157-page decision.