William Byrd High School students who have not gone to class this week will not be penalized for their absences, Principal Richard Turner said at the Roanoke County School Board meeting Thursday night.

More than 200 students at the roughly 1,200-student school have stayed home since it came to light last Friday that some people at the school have been experiencing inexplicable twitching symptoms.

Turner said absences would be excused until today.

"Past Friday, we expect everybody to be at school," he said.

The principal's statement did not reassure some students at the meeting who said they were considering transferring to another school.

"I'm getting so mad at this point," said Joe Bradshaw, a sophomore who hasn't been to school this week.

Parents again criticized the school system for its reluctance to release details about the mysterious symptoms until last week even though school officials received the first report in September.

Several parents at the meeting said they did not want their children back inside the William Byrd High School building, which dates to 1969.

"I want them either to give them an alternative place to go to class or close it down until they find out what's going on," said Sherry Beckner, a parent.

Angela Bradshaw, Joe's mother, said about 150 parents had consulted with a lawyer.

In response to the criticism, the school system released a statement saying it was advised by the Virginia Department of Health not to be specific about the symptoms because of medical privacy laws. Bobby Parker, a health department spokesman, confirmed the school system's account.

The statement also confirmed for the first time that a teacher was among those affected.

"The teacher involved has been cleared by doctors at the UVa Medical Center to return to work," it said.

All told, fewer than 10 people have been affected.

The health department is leading an epidemiological investigation to try to determine how people with the symptoms came to be affected, said Stephanie Harper, the district health director. So far, nobody has been able to say what is causing the students to twitch, even though rumors have been rampant.

The school system is also working with environmental consultants to perform tests inside and around the school. Results of those tests should be available today or Monday, said Roanoke County Superintendent Lorraine Lange.