CHARLOTTE, N.C. -- A Charlotte teacher is making national headlines after an op-ed he wrote about arming teachers prompted a mean-spirited email from a stranger.

The Waddell Language Academy teacher turned it into a lesson for his students and the outcome surprised everyone.

"He was a jerk," 7th-grader Matthew Isaacson said on the person who made fun of his teacher.

The email called the teacher, Justin Parmenter, a "wuss," saying he looked like he had always been picked on and "never seen a barbell."

Parmenter’s photo was posted alongside the op-ed he wrote in the Charlotte Observer saying it was a bad idea to arm teachers.

"I felt like it was an outlandish idea but if it was gonna be legitimized at that level, someone needed to take a thoughtful, measured approach to what that would look like in the classroom," Parmenter said.

He got a ton of responses, one of which was filled with a lot of grammatical mistakes.

"It included a lot of personal insults," Parmenter said.

So Parmenter decided to use the email as a lesson for his students.

"We could talk together about what was wrong with it and how could it be made stronger," Parmenter said.

"We went over the errors and highlighted them," Isaacson said.

Instead of being aggressive with his criticism, he could have been constructive with his criticism.

"There was only one thing about the topic and the rest was just criticizing," Isaacson said. "I thought this guy was sort of a jerk and it wasn’t very kind of him to do that."

Next, Parmenter wrote a blog about the whole experience and The Washington Post published it. Then, he sent the link of the Washington Post article to the author of that mean-spirited email.

"I was shocked by his response," Parmenter. "He said he appreciated what my students had to say about his email, he apologized said he spoken hastily and emotionally and he regretted it."

Parmenter said he learned perhaps the greatest lesson of all.

"It sounds cheesy but I would say to a degree it restores my faith in humanity," Parmenter said. "From his email, it sounded like he learned it was possible for people who disagree to treat each other with respect."