The Carroll County School Board plans to end its partnership with the contractor that operates Virginia’s largest full-time statewide virtual school, effectively shutting down a program that serves more than 350 students.

The decision to close what was also the state’s first online school deals a blow to Gov. Robert F. McDonnell’s goal of expanding virtual education options. It also leaves hundreds of families, including many in Northern Virginia, in the lurch for the coming school year.

“Carroll County has definitely pulled the rug out from [under] everyone,” said Cherie Nielsen, a parent leader of the Virginia chapter of Public School Options, an advocate for nontraditional public schools. “We are scrambling.”

The School Board in the southern Virginia county voted in mid-April to discontinue the contract, citing administrative and liability concerns. But families around the state did not find out about the change until late last week, when they received an e-mail from the Virginia Virtual Academy.

Jeff Kwitowski, a spokesman for K12 Inc., the Herndon-based company that operates the school, said the decision also came as a surprise to the company. “We are aggressively looking for a new partnership” to keep the school open, he said.

Taxpayer-supported, privately operated virtual schools have been receiving increased public scrutiny, including criticism of their performance and their funding arrangements.

Last year, a K12 shareholder filed a class-action suit alleging that the company had made false statements about students’ academic performance. The company agreed to a $6.75 million settlement this spring.

About 275,000 students nationwide are enrolled in full-time, publicly funded virtual schools, and enrollment has been growing about 30 percent a year, according to Susan Patrick of the International Association for K-12 Online Learning, a trade association.

Virginia offers online courses through the state’s Department of Education, and many districts, including the Fairfax County school system, are creating virtual schools available to their own students.

But the Virginia Virtual Academy, which opened in 2009, was the first attempt to offer a full-time program to students statewide. A second statewide program opened in 2012 and serves about 130 students through a partnership between K12 and King and Queen County. Another statewide school was briefly available through the school system in Buena Vista City, near Lynchburg, but the contract was not continued.

Developing such programs often proves difficult as online communities of students and teachers try to take root in school systems that have long operated brick-and-mortar schools at local taxpayer expense and with local school board control.

Some states have created statewide school districts to oversee virtual schools, but Virginia’s constitution gives local governments jurisdiction over public education. So K12 must offer its online curriculum through local school districts.

The partnership with rural Carroll County had a distinct financial advantage for the for-profit company. Carroll County receives more in per-pupil state aid than most districts, because of a formula that favors poorer districts, and all of the virtual academy’s students are counted as Carroll students, regardless of where they live.

Carroll County also stood to gain from the relationship because it collected a $500 registration fee and a small management fee for out-of-district students.

After four years, school officials found that program costs were mounting and that administrators were putting in extensive time working with 29 other school districts to sort out complex special education accommodations and comply with other government rules.

They also were concerned about being held liable for students who were not in the county. Lawyers advised county officials that they could be held responsible if special education plans were not upheld, for example.

“We had more than 350 students in the program, and only five were Carroll County students,” School Superintendent Strader Blankenship said. “We were spending a lot of time on students that were not Carroll County students.”

The situation in Caroll County has renewed calls for the state legislature to find a more permanent solution to funding and operating statewide virtual schools.

The General Assembly has debated for several years how to pay for students who move between districts and make the jump from traditional schools to computer-based schools. There are questions about the fair price for educating students who don’t need classrooms, school lunches or bus rides and about who should foot the bill.

The parents say they want a lasting answer.

“It’s one year to the next,” said Rachelle Berry-Bissessar, an Ashburn mother with two sons enrolled at the virtual academy and a third she was hoping to enroll in the fall. She said she is tired of holding her breath every spring when the K12 contract comes up for renewal.

She opted for the virtual academy after her oldest son had a bad year in first-grade at a neighborhood school in Fairfax County, where the family lived at the time.

“I sent him off to school already reading and enthusiastic,” Berry-Bissessar said. “By November, he was in tears every morning, and by January, he did not want to go any more.”

After she started teaching him at home through the virtual academy, he blossomed again academically and emotionally, she said.

“I think it’s really unfair to remove this option for the kids that it’s working for,” she said.