The lone suspected gunman was also dead, though it's unclear whether the student committed suicide. Authorities say no shots were fired by law enforcement. Names of the suspect and the school employee haven't yet been released.
"In my estimation, he is a hero ... We do know he was trying to intervene," Reno Deputy Police Chief Tom Robinson said about the fallen staff member.
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.
A motive for the violence was unknown.
"As you can imagine, the best description is chaos," Robinson said. "It's too early to say whether he was targeting people or going on an indiscriminate shooting spree."
Police said between 150 and 200 officers, including some from as far as 60 miles away, responded to the shooting.
Students from the middle school and neighboring 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 and ended outside the school building itself, according to police.
"I was deeply saddened to learn of the horrific shooting at Sparks Middle School this morning," Nevada Gov. Brian Sandoval said in a statement. 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.
In a statement on the website of Sandy Hook Promise, a gun control advocacy group, Nicole Hockley, whose son Dylan was killed in the shooting said, "It's moments like this that demand that we unite as parents to find common sense solutions that keep our children_all children_safe, and prevent these tragedies from happening again and again."
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.
Mayor Geno Martini spoke at a morning press conference to assure residents that the community was safe.
"It's a tragic day in the city of Sparks," he said. "This is just an isolated incident."
Associated Press Writer Michelle Rindels contributed from Las Vegas.