In the weeks following the Sandy Hook massacre, a number of state lawmakers' proposals to fight school gun violence by arming teachers have been met with staunch opposition. But what many don't realize is that more than one-third of all states already allow teachers and adults to carry guns on school grounds.

Across the country, 18 states allow adults to carry a loaded gun on school grounds, generally provided that they have written permission from a principal or the school board, NBC News reports. The laws don't necessarily specify exact reasons for giving teachers or adults the authorization to carry, but some do also include provisions for permissible activities like safety demonstrations or ceremonies.

But like one Utah educator who has expressed her newfound desire to carry a firearm at school, many are unaware of the state laws that have provisions permitting adults to carry on campus.

In an email obtained by Gawker, Oregon state Rep. Dennis Richardson (R) tells three superintendents that teachers should be allowed to carry guns on campus, and that armed teachers could have prevented the massacre in Connecticut.

Oregon school boards, however, are already allowed to authorize teachers and other adults to carry guns on school grounds.

And while teachers -- along with the nation's two largest teachers unions -- have generally come out against arming educators, one school in Texas has permitted concealed carry by teachers for years. The principal calls it "a policy that would protect."

Below, the 18 states that allow teachers or other adults to carry loaded firearms on school grounds:

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  • Alabama

    Prohibits possessing a firearm on school grounds only if the carrier has "<a href="http://www.legislature.state.al.us/codeofalabama/1975/13A-11-72.htm">intent to do bodily harm</a>"

  • California

    Permits carrying a firearm on school grounds if a person has "<a href="http://www.leginfo.ca.gov/cgi-bin/displaycode?section=pen&group=00001-01000&file=626-626.11">the written permission of the school district superintendent, his or her designee, or equivalent school authority</a>."

  • Connecticut

    Permits carrying a firearm on school grounds <a href="http://www.cga.ct.gov/2011/pub/chap952.htm#Sec53a-217.htm">if agreed to by school officials.</a>

  • Hawaii

    Generally <a href="http://smartgunlaws.org/guns-in-schools-in-hawaii/">does not prohibit</a> the carrying of guns in schools.

  • Idaho

    Permits carrying a firearm on school grounds "as an appropriate part of a program, an event, activity or <a href="http://www.legislature.idaho.gov/idstat/Title18/T18CH33SECT18-3302D.htm">other circumstance approved by the board of trustees or governing board</a>."

  • Iowa

    Permits carrying a firearm on school grounds if "<a href="http://coolice.legis.iowa.gov/cool-ice/default.asp?category=billinfo&service=iowacode&ga=83&input=724.4B">a person has been specifically authorized by the school</a>."

  • Kentucky

    Permits carrying firearms on campus if the person has been "<a href="http://www.lrc.ky.gov/krs/527-00/070.PDF">authorized to carry a firearm by the board of education.</a>"

  • Massachusetts

    Permits carrying firearms on school grounds with the <a href="http://www.malegislature.gov/Laws/GeneralLaws/PartIV/TitleI/Chapter269/Section10">authorization of the school board or principal</a>.

  • Mississippi

    Permits carrying firearms on campus in a "<a href="http://www.healthyschoolsms.org/healthy_school_environment/documents/SchoolSafetyManual20082.pdf">school-approved program conducted under the supervision of an adult</a> whose supervision has been approved by the school authority.'

  • Montana

    Permits carrying firearms on school grounds with the <a href="http://data.opi.mt.gov/bills/mca/45/8/45-8-361.htm">permission of a school district's trustees.</a>

  • New Hampshire

    <a href="http://smartgunlaws.org/guns-in-schools-in-new-hampshire/">Does not have a law</a> prohibiting non-students from possessing firearms on school grounds.

  • New Jersey

    Permits carrying firearms on school grounds with "<a href="http://essexcountynjcriminalattorneys.wordpress.com/about/n-j-s-a-2c39-5-unlawful-possession-of-a-weapon-new-jersey/">the written authorization of the governing officer of the institution</a>."

  • New York

    Permits carrying firearms on school grounds with <a href="http://www.nycourts.gov/cji/2-PenalLaw/265/265-01%283%29.pdf">written authorization from the school.</a>

  • Oregon

    Permits carrying guns on school grounds<a href="http://www.dennisrichardson.org/firearm_survey.pdf"> with authorization from the school board</a>, or the "agency that controls the public building."

  • Rhode Island

    Permits carrying firearms on school grounds <a href="http://webserver.rilin.state.ri.us/Statutes/title11/11-47/11-47-60.HTM">with a state concealed weapons permit.</a>

  • Texas

    Permits carrying firearms on campus with <a href="http://www.statutes.legis.state.tx.us/Docs/PE/htm/PE.46.htm">written authorization from the school.</a>

  • Utah

    Permits carrying firearms on campus with the approval of the "<a href="http://le.utah.gov/code/TITLE76/htm/76_10_050505.htm">responsible school administrator</a>"

  • Wyoming

    <a href="http://smartgunlaws.org/guns-in-schools-in-wyoming/">Does not have a general prohibition</a> on the possession of firearms on school property, but bars concealed weapons with or without a permit.