David Drayton pleaded guilty to voluntary manslaughter and was sentenced in Richmond County Superior Court by Judge Sheryl Jolly.
Mr. Drayton was 14 when he attacked teacher Linda Gail Hendrick in 1999.
Ms. Hendrick, 59, was found in a pool of blood at the school, where she taught special needs children, including Mr. Drayton.
Mr. Drayton was 14 at the time. Because of his age, he could not be prosecuted as an adult for aggravated battery. The charge against him was handled through the juvenile court system, and he was committed to a juvenile detention facility for the maximum possible, five years.
Ms. Hendrick remained in a coma from Nov. 22, 1999, until her death on May 31, 2007.
She had suffered about 70 stab wounds from a pair of scissors and a massive head injury in the restroom near her eighth-grade classroom.