A Harris County jury imposed the sentence against Luis Alfaro, hours after finding him guilty of manslaughter in the death of 17-year-old Joshua Broussard. The two had fought during a brawl last September at Spring High School.
Broussard was stabbed multiple times and bled to death minutes later.
Jurors had the option of convicting Alfaro of the more serious offense of murder, which could have resulted in a life sentence.
"There's no words to describe that, because he knows that he didn't commit that," said Alfaro's mother Maria Alvarenga.
Sheriff's investigators have blamed gang rivalry for the fight and say an altercation the day before prompted the melee Sept. 4 at the school north of Houston.
"Innocent people shouldn't be dead because of your actions, because you want to be bad at school," said Broussard's mother Stephene Dickerson.
Defense attorney Milan Marinkovich had argued video footage showed Alfaro, who was 17 when the stabbing occurred, didn't have enough time to inflict fatal wounds.
School officials temporarily imposed tightened security in the aftermath of the fight. The school used portable metal detectors and hand-held wand security devices to screen people. Also, students had to carry their stuff in clear backpacks or zip-lock bags.
The Spring Independent School District is issuing the following statement after the verdict was reached:
"The death of Joshua Broussard was a tragedy for the entire Spring community. Our hearts are with all the students and their families who were impacted by the incident that occurred on Sept. 4, 2013. The district has worked with Spring High School and our community to promote healing and increase safety in the aftermath of the incident and will continue to do so as we move forward following the jury's decision today."
The Associated Press contributed to this report