"There are evil people in the world - there are evil people everywhere," says Mike Magowan, who is training teachers how to use guns in the US state of Florida.
Mr Magowan, who runs the Veritas Training Academy, has been offering teacher-only firearms classes since the massacre at Sandy Hook Elementary School, Connecticut, in December 2012. The classes have proven incredibly popular among teachers who fear a similar incident in their corridors and classrooms.
"There are stupid people out there who want to make themselves famous by hurting kids," says Mr Magowan. "Sandy Hook opened the eyes of a lot of people - that there's evil in the world."
In his classes, teachers are primarily taught about safety and the basics of defending themselves against armed intruders, learning how to use chairs, pens and other instruments to fight off an attacker. But the lessons also cover the use of firearms and how to accurately aim a gun in threatening circumstances.
"I demand that teachers, the people who are looking after my kids, are highly trained in firearms, because [if there is an armed intruder] all the police are going to do is turn up and write a report," Mr Magowan says. "I don't want a teacher who has a permit and thinks they're a gunfighter. That will just mean one more for the body count. I train teachers to shoot the dog and protect the flock."
The rising number of people walking through Mr Magowan's door is representative of a wider movement of teachers seeking to arm themselves.
The massacre at Sandy Hook - where 20 children and six teachers were killed by a lone gunman, 20-year-old Adam Lanza - has seared itself on to the national psyche of the US, sparking a national debate on gun ownership that still rages.
Startlingly, the broad response to Sandy Hook, particularly among legislators, has been in favour of more guns in schools, not fewer. From the start of the new academic year, adults in 28 states will be legally permitted to carry firearms on school grounds. In seven of these states, the law specifically says that teachers will be allowed to bear arms in schools.
However, in most of these states, teachers will be under no obligation to tell their principal if they are carrying a weapon. Parents could be sending their child into school without a clue that the kindergarten teacher is armed.
And from Texas to Utah, Colorado to Missouri - where heavily armed police have been criticised for shooting two black youths in Ferguson, St Louis - teachers are choosing to learn how to shoot and carry a weapon, fearing that they will one day need to protect students from an armed intruder.
Early last year, just one month after the Sandy Hook shooting, the largest teaching union in the US, the National Education Association, surveyed its members to get a sense of their attitudes towards guns, particularly in schools.
Of the 800 teachers polled, 90 per cent supported the use of background checks on people who wished to buy guns, and 76 per cent backed the prohibition of military-style weapons - such as those used by Lanza at Sandy Hook - outside the police and the military.
But the survey highlighted the peculiar relationship that the US has with guns: 22 per cent of the polled teachers were in favour of allowing teachers and other school staff to be trained in the use of firearms, and permitting them to carry the weapons in schools.
According to Lily Eskelsen Garca, president-elect of the National Education Association, "adding guns to prevent gun violence in schools only exacerbates the problem".
"Let's dismiss these dangerous ideas and focus on measures that will create safer learning environments, instead of turning our schools into the Wild West," she adds. "Let's make it more difficult for guns to enter our schools, not easier."
It is not just teachers who are taking firearms seriously: officials in school districts in some of the biggest US cities are voting in favour of a more heavily armed security force.
Last week, the eight-member board of the Compton Unified School District in California voted in favour of arming its school police officers with rifles usually reserved for use by the US Army.
This means that police officers are now able to patrol the corridors and campuses of Compton's schools while carrying AR-15 rifles, weapons that are capable of firing 800 rounds per minute.
Compton has become the sixth school district in and around Los Angeles to vote in favour of arming the officers charged with protecting the city's students with military-grade weapons. The reason given by the board - and subsequently the school district police department - for the decision was simple: fear of an armed intruder.
In a statement, the police department's union, the Compton School Police Officers' Association, says the police-issue firearms that its members currently carry would be ineffective against a gunman wearing body armour.
"If we encounter an active mass murderer on campus with a rifle or body armour, our officers may not adequately be prepared to stop that suspect," the union says in its statement. "School police officers will undergo a training course, followed by a shooting proficiency test on a firing range and a written exam."
It adds: "The rifles are designed for increased accuracy and use rifled ammunition that can pierce body armour. The safety of our students, staff and parents is very important to us."
But for thousands of teachers and people like Mr Magowan, a heavily armed police force does not guarantee peace of mind. "Why not make the teacher the armed specialist?" Mr Magowan says. "I would feel safer if I knew my kid's teacher was carrying a gun."