D'Wayne Johnston, 49, told The Associated Press in a telephone interview that he brought the weapon to Tioga High School on Oct. 2 because of a threat made by the boy a day earlier that resulted in the student's expulsion. The school board later accepted Johnston's resignation, which is effective at the end of the year.
Tioga Police Chief Sean Duisen said investigators would look into whether Johnston broke any laws, though district officials had not reported it as a crime.
North Dakota was one of several states where legislatures discussed gun laws after last winter's elementary school shooting in Newtown, Conn. North Dakota's Republican-controlled Legislature ultimately rejected a measure that would have allowed people with concealed handgun permits to carry their weapons in schools.
Johnston would not go into detail about the threat but said the student in question had previous discipline problems.
"It led me to believe that a much heighted level of student and staff safety as well as my own was necessary," he said.
"I wouldn't venture into a decision like this lightly. But it was a decision I made on my own."
Johnston now says he should have instead talked to police and asked them for help. Johnston acknowledged carrying the gun after several people noticed it. He then offered to resign, prompting the school board to hold an emergency meeting last Friday.
The Tioga Tribune first reported the story and covered Friday's emergency school board meeting.
Jossie Nielsen, who has two children at the school, said she's concerned that that some school board members might not be aware of the details of how the situation with Johnston is being handled. Nielsen said that while her son was unfazed by the incident, her daughter was surprised.
"Not that she doesn't feel safe," said Nielson, 39, "but he felt the need to bring the gun."
School board President Mark Schmidt, who has two children in the high school, said he's still getting calls from people who are divided about whether Johnston should leave now or be allowed to finish out the school year.
"Right now, I do not believe he is a danger to anyone and he admitted to the wrongdoing," Schmidt said in explaining the decision to allow Johnston to remain for now.
Also, a school principal is on medical leave, he said. And the school staff is facing increased pressures because the district's enrollment roughly doubled within the past three years amid a huge oil boom in western North Dakota, Schmidt said. The district now has nearly 500 students.
Duisen said police haven't received a formal complaint about the incident and that he only learned about it when he read a story in the local paper.
Schmidt said the board plans to assemble a school safety committee at its next meeting.
"We've been a little corner of the country that has not been affected like the rest of the world. And things are just catching up fast here," Nielson said.
Johnston, who has been at the Tioga district nine years, six as superintendent, said he plans to stay in education.
"What I did was not an appropriate way to deal with school safety," Johnston said. But he said he hopes good comes from it, including a better understanding of where students are coming from and how community resources can help everyone, "so no one person has to feel like they have to take it on themselves."