Academic Magnet High and other Charleston County magnet schools will have to open their doors to non-county students who own property in the county, according to a state Supreme Court ruling issued Wednesday.

Three of the court’s five justices agreed that the school district can’t “monopolize” its magnet schools for county residents when state law gives student property owners who live elsewhere the right to attend Charleston schools.

“The Board can most certainly set admissions requirements for its magnet schools and even set geographic priority for available seats,” according to the opinion. “What it cannot do is exclude an entire segment of students recognized under the statute as qualified to attend its schools.”

That means students who don’t live in Charleston County still have to go through magnet schools’ admissions processes and meet acceptance criteria. And to be eligible as a non-county resident, students must own a piece of county property assessed at $300 or more.

The decision is the result of a case filed in June 2010 by a former Berkeley County parent and attorney, Gayla McSwain. She sued Charleston County schools over her daughter’s right to attend Academic Magnet High, which is one of the top-rated magnet schools in the country.

The school district argued that it had the right to establish attendance requirements for its magnet schools, and that magnet students must live in the county.

The court majority wrote that it wasn’t unsympathetic to the district’s assertion that non-resident children are displacing qualified resident children, but “we are constrained to interpret the unambiguous language” in the law. And the school board can’t unilaterally exclude children who are qualified to attend its schools, they wrote.

“If this interpretation is contrary to legislative intent, or if it does not promote the furtherance of education, we leave it to the legislature to amend the statute,” according to the majority opinion.

Justices Donald Beatty and Costa Pleicones wrote dissenting opinions, and both said the court historically has deferred to a local government’s control over the operations of its public schools.

They both said the court should continue that deference and give the Charleston school board the discretion to establish admissions criteria and decide where students should attend.

Both also said the General Assembly has explicitly given full authority to local boards to set attendance criteria.

McSwain wrote in an email to The Post and Courier that the ruling ensures that parents who can’t afford to move to a different school district no longer are forced to leave their children in bad or mediocre schools. The court recognized that all children, regardless of their socioeconomic circumstances, are entitled to the opportunity to attend the school of their choice, she wrote.

“Students who work hard and meet the acceptance criteria for South Carolina’s best schools should never be excluded from those schools due to illegal, exclusionary school board policies,” she wrote.

Scott Price, an attorney for the S.C. School Boards Association, said this might be an issue the association looks at and tries to address with lawmakers. This could end up limiting students’ choices rather than expanding them, he said.

“That’s problematic,” he said. “That takes us a step back from where we’re all wanting to head in providing more choices. It could have a chilling effect.”

Out-of-county students must own property; they can’t just pay tuition to enroll in magnet schools. The majority found that tuition can be imposed on non-resident children to reimburse the district for the educational costs not covered by the children’s property taxes.

The school board will charge tuition starting in 2013-14 to new out-of-county students who own property and attend Charleston schools. The amount will vary, but it’s roughly equivalent to the district’s average revenue per child — that was roughly $6,400 last year — minus the total of property taxes the student paid.

School officials said they didn’t know Wednesday how many out-of-county students were enrolled at Academic Magnet High. In the fall of 2011, there were seven.

Charleston school leaders had little to say about the ruling. They said they needed more time to read and understand the court’s opinion.

John Emerson, the district’s attorney, was in a daylong mediation hearing and declined to comment. Superintendent Nancy McGinley said Emerson hadn’t had time to read the ruling, which involves complicated issues, and she wanted to wait to comment until she fully understood its ramifications.

“This is going to be John’s top priority,” she said.

School Board Chairwoman Cindy Bohn Coats said it is premature to have any conversation about the future until she had a better handle on the ruling.

Coats said this case speaks volumes about the desirability of the county’s magnet schools, and its challenge is to ensure every school is as sought after and high-quality as Academic Magnet High.

“We need to take our won examples of success and duplicate it,” she said.

Reach Diette Courrégé Casey at @Diette on Twitter or 937-5546.