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(NEXSTAR) – Following a shooting that left six dead, including three children, at The Covenant School in Nashville, there have been renewed calls to have armed teachers in schools. Some states have already enacted laws allowing this while others are hoping to do so.

In 2013, just a few months after the deadly Sandy Hook shooting in Newtown, Connecticut, South Dakota became the first state to enact a law allowing school employees to carry guns, The New York Times reports.

Since then, roughly 30 states have enacted similar legislation, according to data collected by the Giffords Law Center.

Only 16 states currently prohibit teachers from carrying a firearm: Alabama, California, Illinois, Louisiana, Maine, Maryland, Mississippi, Nebraska, New York, North Carolina, North Dakota, Rhode Island, Virginia, Washington, West Virginia, and Wisconsin, as well as the District of Columbia.

Tennessee allows teachers at private schools to carry if that school gives them permission but doesn’t allow it in most public schools. Before March’s school shooting at the Covenant School in Nashville, some state lawmakers were pushing a bill that would have expanded gun-carrying access for teachers, WKRN reports. Out of respect for the victims, lawmakers delayed debating the bill.

Mississippi lawmakers recently passed a bill that would allow armed, trained teachers within its schools. It awaits approval from Governor Tate Reeves.

For those states that do allow teachers to carry, many require them to have permission from the school or district, if they are part of a certain program or if they have a concealed carry license.

In Alabama, for example, some school administrators are allowed to have a firearm on campus if they complete certain training through the state’s sentry program and there isn’t a school resource officer available, according to a report by the RAND Corporation.

Oklahoma lawmakers recently passed a bill that would add a concealed carry license to the list of licenses teachers could get in order to be armed on campus, according to KFOR. The bill passed the House and has been sent to the Senate.

Lawmakers in Indiana, where teachers are allowed to carry firearms, are hoping to pass legislation that would create training standards for teachers and have the state pay for educators to undergo handgun training, WXIN reports. The bill passed the House and was sent to the Senate in February.

If schools have security that is non-law enforcement, most states have elected to allow them to carry firearms, according to Giffords Law Center’s report. As with arming teachers, most states require the school or school district to grant permission for the security guard to carry. The exceptions include Georgia, Iowa, Michigan, and Nevada, which allow it without permission.

Washington state will only allow it if the security officer has completed training equivalent to that received by law enforcement. Virginia allows non-law enforcement security to have a firearm at religious schools with authorization from the school but prohibits it at public schools.

Those states that do not allow non-law enforcement security personnel to carry on school grounds are Alabama, Maine, Nebraska, North Carolina, Rhode Island, West Virginia, and Wisconsin, according to data collected by Giffords Law Center.

Four of those states – Maine, Nebraska, West Virginia, and Wisconsin – currently have laws that do not allow any non-law enforcement security, teachers, or other school employees to carry on campus. West Virginia does, however, allow people with concealed carry permits to bring firearms onto public college and university campuses.

Hawaii, according to the Giffords Law Center, has no legislation related to arming teachers or other individuals on school campuses.

While there is little evidence to be had from studies on the efficacy of arming teachers against potential school shooters, the idea that ‘good guys with guns stop bad guys’ may not actually be the case.

In a review of states that enacted right-to-carry handgun laws between the 1970s and mid-2010s, Stanford University found a 13-15% increase in violent crimes in the 10 years after the legislation was passed.

In some cases, like the 1999 Columbine High School shooting, armed guards were at the school but unable to stop the shooters, CNN reports.

Russell Falcon contributed to this report.