The suspected gunman was also dead, and authorities say no shots were fired by law enforcement.
Two other students were critically injured in the violence that erupted around 7:15 a.m., shortly before classes began Monday. One is out of surgery and the other is doing well, according to police.
Police said between 150 and 200 officers responded to the shooting.
Students from the middle school and next door elementary school were evacuated to the nearby high school, and classes were canceled.
At the evacuation center, parents walked with their arms around their children, some of whom were in tears.
"We came flying down here to get our kids," said Mike Fiorica, whose nephew attends the school. "... It's really chaotic. You can imagine how parents are feeling. You don't know if your kid's OK."
The shooting happened on the school's campus, but outside the school building itself, according to police.
Gov. Brian Sandoval issued a statement after hearing about the shooting.
"I was deeply saddened to learn of the horrific shooting at Sparks Middle School this morning. My administration is receiving regular updates and the Nevada Highway Patrol is assisting at the scene," he said. Sandoval extended his thoughts and prayers to those affected.
Senate Majority Leader Harry Reid, D-Nevada, offered his condolences to students, parents and staff who experienced "a traumatic morning."
"No words of condolence could possibly ease the pain, but I hope it is some small comfort that Nevada mourns with them. I stand by to be of any assistance if there is anything that can be done," Reid said in a statement.
The school, located in a working class neighborhood, enrolls about 700 students in 7th and 8th grades.
The violence erupted nearly a year after a gunman horrified the nation by opening fire in Sandy Hook Elementary School in Newtown, Conn., leaving 26 dead. The Dec. 14 shooting reignited debate over how best to protect the nation's schools and whether armed teachers should be part of that equation.
Washoe County School District held a session in the spring in light of the Connecticut tragedy to educate parents on what safety measures the district takes.
Sparks, a city of roughly 90,000 that sprung out of the railway industry, lies just east of Reno.
Associated Press Writer Michelle Rindels contributed from Las Vegas.