RITTMAN, Ohio >> Mandi, a kindergarten teacher in Ohio, had already done what she could to secure her classroom against a gunman.

She positioned a bookcase by the doorway, in case she needed a barricade. In an orange bucket, she kept district-issued emergency supplies: wasp spray, to aim at an attacker, and a tube sock, to hold a heavy object and hurl at an assailant.

But after 19 children and two teachers were killed in Uvalde, Texas, she felt a growing desperation. Her school is in an older building, with no automatic locks on classroom doors and no police officer on campus.

“We just feel helpless,” she said. “It’s not enough.”

She decided she needed something far more powerful: a 9 mm pistol.

So she signed up for training that would allow her to carry a gun in school. Like others in this article, she asked to be identified by her first name because of school district rules that restrict information about employees carrying firearms.

A decade ago, it was extremely rare for everyday school employees to carry guns.

Today, after a seemingly endless series of mass shootings, the strategy has become a leading solution promoted by Republicans and gun rights advocates, who say that allowing teachers, principals and superintendents to be armed gives schools a fighting chance in case of attack.

At least 29 states allow individuals other than police or security officials to carry guns on school grounds, according to the National Conference of State Legislatures. As of 2018, the last year for which statistics were available, federal survey data estimated that 2.6% of public schools had armed faculty.

The count has probably grown.

In Florida, more than 1,300 school staff members serve as armed guardians in 45 school districts, out of 74 in the state, according to state officials. The program was created after a gunman killed 17 people at Marjory Stoneman Douglas High School in Parkland in 2018.

In Texas, at least 402 school districts — about one-third in the state — participate in a program that allows designated people, including school staff members, to be armed, according to the Texas Association of School Boards. Another program, which requires more training, is used by a smaller number of districts. Participation in both is up since 2018.

And in the weeks after the Uvalde shooting, lawmakers in Ohio made it easier for teachers and other school employees to carry guns.

The strategy is fiercely opposed by Democrats, police groups, teachers unions and gun control advocates, who say that concealed-carry programs in schools — far from solving the problem — will only create more risk.

Past polling has shown that the vast majority of teachers do not want to be armed.

The law in Ohio has been especially contentious because it requires no more than 24 hours of training, along with eight hours of recertification annually.

Studies on school employees carrying guns have been limited, and research so far has found little evidence that it is effective. There is also little evidence that school resource officers are broadly effective at preventing school shootings, which are statistically rare.

Yet arming school employees is finding appeal — slight majorities among parents and adults in recent polls.

Of the five deadliest school shootings on record, four — in Newtown, Conn.; Uvalde; Parkland; and Santa Fe, Texas — have happened in the past 10 years.