Sparks police have identified the two deceased victims as a staff member and the shooter. Police said the shooter died of a self-inflicted gunshot wound.
Students who witnessed the shootings told local media outlets that the shooter was a seventh grade boy who may have been bullied in the past.
Police say the staff member was killed while trying to shield students. His family has since identified him as 45-year-old math teacher Michael Landsberry.
"In my estimation he's a hero," Reno's Deputy Police Chief Tom Robinson said at a news conference.
Landsberry was a military veteran who leaves behind a wife and two stepdaughters.
Authorities responded to the school around 7:15 a.m. Monday, 15 minutes before the first classes were set to begin.
The shooting reportedly took place on the middle school's campus but outside the school building itself, which enrolls about 700 seventh and eighth graders.
Students say they watched as the shooter fired several shots.
"I was on the basketball court and I heard the first shot. I looked over and I saw a kid, my best friend KJ, lying on the ground shot in the arm," said one student. "We heard another one and this time it was against a teacher. He got shot straight in the chest."
Two male students, both 12 years old, were injured and taken to Renown Regional Medical Center following the shooting. Police said both boys sustained non-life-threatening injuries. One boy was shot in the shoulder and the other was shot in the abdomen. They were in stable condition.
Washoe County School District spokesman Charles Rahn says the middle school and the adjacent Agnes Risley Elementary School were evacuated to Sparks High School.
Officials said at an afternoon press conference that the middle and elementary schools will be closed for the remainder of the week.
Parents were slowly allowed to pick up their children.
"Students are safe and the community is safe," said Sparks Police Chief Brian Allen. "There are no outstanding suspects. The students are in the process of being reunited with their parents at this time."
One student talked to The Reno Gazette-Journal and described hearing the first shots.
"We heard a pop, like a loud pop, and everybody was screaming and the teacher came to investigate. I thought it was a firecracker at first but the student was pointing a gun at the teacher," said 13-year-old Kyle Nucum. "After the teacher told him to put it down, the student fired a shot at the teacher. The teacher fell and everybody ran away."
Nucum says as he and some of his fellow students attempted to flee somewhere safe, they heard about four or five additional shots.
This shooting comes less than a year after a gunman opened fire at Sandy Hook Elementary School in Newtown, Conn. on Dec. 14, 2012. That shooting left 20 children and six adults dead.
Police are hoping to interview the estimated 20 to 30 witnesses who heard or saw gunfire as they waited for the morning bell to ring at 7:30 a.m.
Robinson said he hoped the interviews would help police determine the suspect's motive and whether he shot indiscriminately or was targeting specific victims.
Sparks is located east of Reno.
ABC News and The Associated Press contributed to this report.