The boy was shot in the torso at 8:09 a.m., moments after being dropped off by an aunt at Benjamin Tasker Middle School in Bowie, Md. The aunt heard a single shot and saw the boy "slump over," said Prince George's County Police Chief Gerald Wilson.
The aunt rushed him to the nearby Bowie Health Center. He was airlifted just before 9 a.m. to Children's National Medical Center in Washington, police said.
A hospital spokeswoman said the boy was in critical but stable condition and was in surgery.
Last week, five people were killed in Montgomery County during a 16-hour period from Wednesday night into Thursday morning. A sixth victim was shot dead Thursday night on a Washington street. A seventh person was wounded Friday in Virginia.
"We're not going to say these cases are linked, we do not have enough information yet," said Capt. Nancy Demme of the Montgomery County Police Department.
The FBI and officers from Bureau of Alcohol, Tobacco and Firearms are also investigating, officials said.
The shooting bore some similarities with last week's sniper attacks. All of the victims had been hit at long-range by a single bullet.
Four of last week's shootings occurred during the morning rush hour. All seven victims were shot while doing routine daily tasks, such as mowing the lawn, pumping gas and loading packages into the car.
Police said they were in the process of analyzing the bullet in Monday morning's shooting to see if it matched the .223 caliber round found in four of the other attacks.
Police also said they were combing the area for leads and were continuing to search for a white box truck seen by a witness speeding from the parking lot of a post office Thursday immediately after a shooting there.
Parents rushed to pick up their children from the 700-student middle school as a wide area was roped off by police as a crime scene. Officials moved schools throughout the area to a lockdown mode, not permitting students to leave the building for lunch or recess.
"The safest place for the children right now is in the schools," said Iris Metts, chief executive officer of Prince George's County schools.
Doug Duncan, Montgomery County executive, said there was a great deal of concern in the area the shooter would strike again.
"It's very frightening. There's widespread fear in this community and its growing," he said.
Calls continued to pour in to a police tips line set up in the area. Moose said that as of Monday morning, there were 952 credible leads being followed up by local, state and federal investigators.
"All of these victims have been innocent and defenseless. But now we are stepping over the line, shooting a kid. Whoever did this, this is getting to be really, really personal," said Montgomery County Police Chief Charles Moose, crying.
Moose added there was not yet any evidence linking Monday's incident to the other shootings.
Senate Democrats to pull all-nighter on climate change
Dennis Rodman pledges to end trips to North Korea