The Roanoke County Public Schools district is paying $29,444 for tests that determined environmental factors were not to blame for the twitching symptoms that affected several William Byrd High School students in the fall.

The school board approved the payment Thursday night.

"We certainly have an obligation to make sure our students are safe," said Jerry Canada, chairman of the school board. "We don't regret spending a penny of that."

Contractors tested the school's air, water, surfaces and mulch and soil after the students reported experiencing seizurelike twitching.

The tests ruled out increased levels of carbon monoxide, mold, pesticides, herbicides and volatile organic compounds as possible causes.

The first report of the unusual twitching symptoms, which officials later said could have been caused by stress, was reported in September.

By late October, fewer than 10 students had reported experiencing the symptoms, which also included severe headaches and dizziness, according to a parent.

The William Byrd community was outraged that neither school officials nor officials from the Virginia Department of Health could release information about the symptoms.

Officials with the school district and the health department said they could not be specific because of health privacy laws. Identifying the symptoms would have identified those affected, they said.

At a meeting in November, the school system, with the permission of an affected student's parent, told hundreds of concerned students and parents that one of the symptoms was twitching.

The department of health and school officials stressed throughout the ordeal that there was no threat to the public and that the school was safe.

The department of health said in late November that the students were not physically sick. The illness was "sociogenic in nature" and may have been triggered by stress.