In the wake of the school shooting in Parkland, Florida, there's a debate growing about what to do to protect students from shootings. President Trump said he's interested in arming teachers and other school personnel -- an idea backed by the National Rifle Association.

At least four states are considering legislation that would allow educators to carry a concealed firearm in schools. Eight states already do.

"I just signed up to teach kids since," said Karl Donnelson, a teacher in Colorado. "As you can see, with all my other jobs sometimes you have to do additional things at small schools, and this is one of them."

Donnelson sat down with CBS News' Nikki Battiste to explain what it's like to carry a gun, while also working as a teacher.

"If you're gonna protect the kids, why not give them a tool to protect them with," he said.

Karl Donnelson talks with CBS News' Nikki Battiste CBS News

Nikki Battiste: How long have you been a science teacher?

Karl Donnelson: This is my third year.

Battiste: How long have you been armed in your classroom?

Donnelson: This is my first year.

Battiste: What kind of gun is it?

Donnelson: It's a glock, 9 millimeter.

Battiste: It's concealed carry.

Donnelson: Correct.

Battiste: Where is your firearm?

Donnelson: Can I show it to you?

Battiste: Yes, please. In your cowboy boot?

Donnelson: That's why I wear boots.

Battiste: You didn't used to wear boots?

Donnelson: No.

Battiste: Is this gun loaded?

Donnelson: There's nothin' in the chamber. The school board would not allow for us to put one in the chamber.

Donnelson volunteered to carry a gun in his classroom, he's one of about 100 armed staff in schools across Colorado.

Karl Donnelson explains what it's like to carry a gun as a teacher CBS News

Battiste: If you heard gunshots right now, what would you do?

Donnelson: Lockdown, immediately, all the classes will have their locked doors. I would run towards the gunfire. Try to find out who it is and take care of it.

Battiste: If an active shooter were to come in, you have to make a split life-or-death decision.

Donnelson: Correct.

Battiste: Are you ready for that?

Donnelson: Yes. My biggest fear is missing and hitting a student. But that's the risk you take by carrying a gun. May I miss? Yeah, possibly. But would you rather have 50 kids killed or one?

Colorado law prohibits firearms in schools, but a loophole lets districts designate armed safety officers. Armed teachers are required to pass a three-day firearms and trauma response course, which includes a simulated school shooting scenario.

Battiste: How often are you being re-trained or refreshing?

Donnelson: Every semester we go in and shoot the 100 percent qualification.

Fifty-five percent of Colorado voters favored allowing teachers and school officials to carry guns on school grounds, according to a 2015 Quinnipiac poll. CBS News sat down with other teachers who are having the same discussion. Some admit they had mixed feelings when it first came up.

"They could shoot our whole building up before we would ever have anybody get here for help," one teacher said.

"As a human being, it was very saddening to me that that's what this has come to," another teacher added.

Despite warning signs in front of the school, parents and staff are not told who is armed.

Karl Donnelson is a science teacher in Colorado CBS News

Battiste: Do you think they have a right to know?

Donnelson: That's up to the school board, administration, and if anybody asks me I tell 'em.

Battiste: A lot of people would say this is a terrible idea.

Donnelson: Yeah, and that's their opinion, and I respect it. But I think our community wants our students protected. We can't afford security guards, and if teachers are willing to and go through the training I think they should have the opportunity to help protect 'em.

Battiste: What is the answer to keep our kids?

Donnelson: There is no answer, and i'm not sayin' we're gonna stop school violence by havin' teachers with weapons, but at least it's a good start. So there is no answer, but this is what we decided as a community and as a school district.

The school has other armed staff. Each had to pass a background check and a psychological evaluation. The superintendent says other schools considering arming their staffs have reached out to him for guidance.