In Ohio, more than 900 teachers, administrators and school employees asked to take part in the Buckeye Firearms Association's newly created, three-day gun training programme, the association said.
In Texas, an $85 Concealed Handgun License (CHL) course offered at no cost to teachers filled 400 spots immediately, forcing the school to offer another class, one instructor said.
"Any teacher who is licensed and chooses to be armed should be able to be armed," said Gerald Valentino, co-founder of the Buckeye Firearms Association. "It should be every teacher's choice."
The December 14 tragedy in Newtown, Connecticut, sparked a national debate about whether to arm teachers, prompting passionate arguments on both sides.
The deaths of 6- and 7-year-old school children led President Barack Obama to promise "meaningful action" to curtail gun violence, while the National Rifle Association has advocated arming teachers and placing trained guards in each of the country's 100,000 schools.
Ohio and Texas are not the first to offer no-cost arms training to teachers. Just days after the Connecticut mass murder, some 200 teachers in Utah underwent free instruction from gun activists.
Critics ridicule arming teachers as a foolhardy idea promoted by overzealous gun enthusiasts, saying it would only add danger to the classroom while distracting teachers from their job of educating children.
Supporters say an armed teacher could have stopped the massacre at Sandy Hook, where a 20-year-old man armed with a military-style assault rifle killed 20 children and six adults before killing himself.
"What we know is that these spree killers are looking for the highest death toll possible. They look for no-gun zones like schools," Valentino said. "It doesn't make sense that we guard our gold with guns and we guard our kids with hope."
The Buckeye Firearms Association, which successfully lobbied for 2004 legislation allowing people to carry concealed handguns, is offering all eligible state educators free admission to what it calls "an intensive three-day class where you will learn many of the same skills and tactics used by first responders."
Of the more than 900 applicants so far, 73 percent were teachers and 10 percent were kindergarten teachers, Valentino said. Sixty percent were male and 51 percent worked in high schools, he said.
GUNS AND THE LAW
Ohio law does not expressly prohibit guns in schools and leaves it to each individual school board to set policy. Ohio Attorney General Mike DeWine referred to teachers as "first responders" after the Connecticut shootings and announced his office would expand safety training for Ohio school employees.
Texas state law allows teachers who have concealed handgun permits to carry weapons into public school classrooms as long as they have permission from the district superintendent.
Measures introduced in the Texas legislature since the Sandy Hook shooting would make it easier to carry firearms onto college campuses and into schools and other public places where weapons are now banned.
Josh Felker, who teaches the firearms classes in suburban San Antonio, said many of the teachers have told him they plan to carry weapons into their classrooms, even at risk of losing their jobs.
"They are upset at what happened, and no one is going to hurt their kids," said Felker, who offered the class to teachers for free over the holiday break. "One teacher said flat out, 'I don't care if the law changes or not, I'm going to take it to school.' Most of them just want to protect their kids."
On Thursday, the Ohio Peace Officer Training Academy will offer its first "Active Shooter Training Response for Educators Course," which up to now has been reserved for police officers.
One Texas superintendent who since 2008 has given permission to teachers with handgun licenses to carry a gun in school is David Thweatt, who heads the rural Harrold Independent School District, about 175 miles (280 km) northwest of Dallas.
"First they have to have a concealed handgun license, they have to be approved to carry on our campus, they have to undergo additional training, and they are limited to ammunition which breaks apart when it hits a hard object," Thweatt said.
He said he decided to allow teachers to carry weapons in class because in his rural district "law enforcement would never make it here on time" in case of an emergency.
Although the names of teachers who carry weapons were meant to remain confidential, their identities were widely known in town, Thweatt said.
Valentino was adamant that Ohio's armed teachers remain anonymous, citing concerns that local media might reveal who was taking the course.
"The idea is for no one to know what teachers might be carrying. It would be very dangerous to identify these teachers. We don't want to put a target on them," Valentino said.
Texas Republican State Representative Debbie Riddle has introduced a measure to require school boards and superintendents to give permission to teachers who have completed the concealed handgun licensing course to carry weapons into the classroom.
"It would have a chilling effect on any copycats who wanted to replicate what was done at Sandy Hook," Riddle said.