A 16-year-old boy who shot and killed his teacher in Estonia's first known school shooting has been sentenced to nine years in prison.

A local court in the town of Viljandi on Tuesday found the defendant guilty of manslaughter with intent to kill his 56-year-old German teacher during class a year ago.

The court said the defense had been unable to back up the claim that the teenager, who was not identified because of his young age, was angered by the teacher's alleged insulting behavior toward him.

The boy, who was 15 at the time of the shooting, used a registered revolver stolen from his father.

According to Estonian law, minors as young as 14 can be sentenced to up to 10 years in prison in cases of manslaughter.