Southern Poverty Law Center

Stacy Dawson, a Missouri high school student, had been told he couldn't attend prom with his boyfriend.

An openly gay Missouri teenager has won the right to attend high school prom with his boyfriend after threatening legal action, the district superintendent said Friday.

Stacy Dawson, a 17-year-old senior at Scott County Central High School in Sikeston, Mo., had been told last year that he couldn't bring his boyfriend due to a line in the school's handbook that said "students will be permitted to invite one guest, girls invite boys and boys invite girls."

When Dawson questioned the policy, he was told by a school administrator that the school board would not consider revising it, according to The Southern Poverty Law Center, a nonprofit civil rights organization representing Dawson. So on Thursday -- Valentine's Day -- Dawson had The Southern Poverty Law Center send a letter to Scott County Central High and the school district threatening legal action.

One day later, the district had good news for Dawson: They were removing the offending line from their handbook, and said the line was never meant to be exclusive in the first place.

"I found out why the stipulation in the student handbook was originally put in there, and it's rather innocent, to be honest," Alvin McFerren, Scott County Central School District superintendent, said. "This was during a time 10-15 years ago that the previous administration was having issues with some of the students trying to come in on either the single rate or the couple rate. They implemented that to make sure they couldn't circumvent the rates that students were supposed to pay as they entered into our dances."

McFerren said Dawson will be allowed to go to prom with his boyfriend.

"It was never intended to be a discriminatory thing," he said. "We want an educational environment for all of our kids and we're not ever going to discriminate as to whether or not the board has the policy and we don't do that based on sexual orientation. Period."

McFerren said he felt the community, which has just over 360 students in the entire district, would take the change well.

"We are a family," McFerren said. "We're such a small school that I don't feel as if there will be any negative reactions whatsoever. It was never intended to be a policy that would create any controversy in the first place."

In a phone call with NBC News on Friday, Dawson said he was "incredibly happy" with the decision and is "really looking forward" to going to the prom with his boyfriend.

"I automatically told my boyfriend," Dawson said. "He was just as happy as I was."

Dawson said many classmates have told him that it’s good he is standing up for what he believes in.

"My classmates have been really supportive," he said.

In its letter to the school and district, the law center had alleged that under a 1969 Supreme Court decision -- Tinker v. Des Moines Independent Community School District -- Dawson's school could not legally censor his right to free expression, including the right to express himself by taking a same-sex date. The Tinker ruling declared that students don't “shed their constitutional rights to freedom of speech or expression at the schoolhouse gates.”

The letter also cited a more recent case out of Mississippi, where a girl sued her high school over a ban on same-sex couples at the prom in 2010. Constance McMillen ultimately won the case against Itawamba County Agricultural High School after a federal judge ruled that the school district violated her constitutional rights to freedom of speech by not allowing her to wear a tuxedo and bring her girlfriend to the prom.

Scott County Central High's prom is scheduled for April 20. Dawson's lawyer said the change was welcome, but that the law center had yet to receive written confirmation the policy has been removed from the student handbook.

"If it is indeed true that the policy has been permanently changed, it represents a big step forward for LGBT (Lesbian, Gay, Bisexual and Transgender) students in a part of the country that frequently lacks community support for students like Stacy," Alesdair Ittelson, staff attorney for the law center, said.

"We wish that schools out there would proactively take these unconstitutional policies off the books," Ittelson told NBC News.

NBC News Staff Writer Vignesh Ramachandran contributed to this story.

This story was originally published on Fri Feb 15, 2013 2:11 PM EST