A knife gets inside a city school, on a day when parents are nervous to send off their kids.

Not again.  On Monday, there was an incident inside a Baltimore City school, this time involving a knife.

"I'm just sad and speechless right now just hearing that something else has just happened," said Tracey McDaniel, a parent at the National Academy Foundation Prep School.    

It seemed to start off friendly at NAF in East Baltimore.  A visitor brought a birthday cake and balloons to a relative but skirted past the front office.

Then a fight broke out with a staff member and the visitor showed a knife.  Both ended up with hand injuries. 

“I'm at a loss for words," said McDaniel.    

McDaniel learned about the incident at the end of the day, on a day when parents are on edge. 

In surrounding counties, police officers stood at schools.  It's just one proactive step following the shooting at Sandy Hook Elementary, where 20 students and six adults were shot and killed with high-powered weapons.

"The children have already asked why is there a police officer and I already said they're out here to say hi to everybody," said Jim Putman, a parent in Rodgers Forge.    

The police chief in Baltimore County is also the chairman of the National Law Enforcement Partnership to Prevent Gun Violence.  He says right now federal law only requires a background check if you buy a gun from a licensed dealer.

"Over 40% of guns are not sold through dealers.  They're private transactions, sold at gun shows and internet sales and classified ads.  You could check Craig's List today," said Chief Johnson.    

Police say the shooter at Sandy Hook used his mom's firearms, which were bought legally.  But Chief Johnson says background checks have stopped the purchase of nearly two million guns from 1994 - 2009.

Back at schools, the conversations are swirling as parents push to prevent school violence.

"We talked about this all day at work," said McDaniel.  "It's a combination of all of it - gun safety, mental health, being proactive," she said.    

Chief Johnson says the shooter who killed three people at a salon in Wisconsin would not have been able to buy a gun if a national law was in place.  He bought it online to avoid a background check.

Chief Johnson says there needs to be a limit on high-capacity ammunition magazines to no more than 10 rounds.