If Christine Lamb was at all nervous, she kept it well hidden all morning. The new principal of Fairfax County's Groveton Elementary School was the picture of enthusiasm yesterday as she greeted parents and students on opening day, helping children find their classrooms and reassuring the mothers of teary-eyed kindergartners.

It was a good first day in a job that promises to be a pressure cooker. On top of the problems facing any new principal, Lamb must raise student achievement to a certain level within three years to be certain of keeping her job. Groveton is one of 20 Fairfax elementary schools that risk having their staffs replaced if they do not meet the school district's performance targets by 2002.

Lamb said she isn't worried. "I've never run from a challenge," she said. "When you have this much expertise in a building and this kind of enthusiasm, I can't see how we can't succeed."

As schools opened yesterday in Fairfax and most of Northern Virginia, the stakes at Groveton were a striking example of the new emphasis on school accountability that has swept the country. Never before has Fairfax, one of the country's most highly regarded school districts, threatened such penalties at any school.

But Groveton and the other 19 schools, which were picked based on their low test scores and their high numbers of students who are low-income or speak limited English, are being given extra resources to meet their goals. And the schools will qualify for rewards if they reach the targets.

Parents dropping off their children at Groveton yesterday were mostly excited about the extra teachers and instructional time that students will be getting this year. The 20 "Project Excel" schools have gone from half-day to full-day kindergarten and stopped the practice of releasing students two hours early on Mondays, as occurs at other Fairfax schools.

"It's bringing in extra resources and positive programs to address our needs--problems that haven't been addressed in the past, like our high ratio of ESL [English as a second language] students, low test scores and areas of poverty in our community," said Carolyn Tabarini, who was in and out of the school throughout the day in her role as a PTA officer. "We're looking forward to a really great year."

For the most part, Northern Virginia school officials reported a smooth opening day. Wayne Mallard, the Area II superintendent in Prince William, said its schools had the usual first-day "hiccups," including buses that arrived at school late, some overcrowded classrooms and a few air conditioners that weren't working. Prince William also had an unprecedented number of school construction and renovation projects this summer, and many of them continued through the Labor Day holiday.

Arlington, like many districts, had to change the start times at some schools because of a bus driver shortage, and many parents were upset by this. Gillian Bristol said that changing the opening bell from 8:10 a.m. to 9:20 a.m. at Abingdon Elementary forced her to drop her son off early at the school's extended day care so she would not be late for work.

Bristol said the school district should pay the extra day-care charges for all parents similarly inconvenienced by the last-minute scheduling changes at Abingdon, Key Elementary and the Arlington Traditional School. School officials have promised to waive only the first month of extra charges.

"My son said to me, 'That doesn't make any sense,' " Bristol said, "and this is a 9-year-old."

At Groveton, in the Alexandria section of Fairfax, more than half the students last year were poor enough to qualify for free or reduced-price lunches, and its student turnover rate is the 10th highest among the county's 133 elementary schools.

Although those are factors that tend to drag down student performance, Lamb and several of her teachers said they are not deterred. In fact, many of the school's 21 new staff members requested assignment to Groveton. And only a small number of Groveton teachers requested reassignment to other schools, Lamb said, with others leaving because of retirement or promotion.

First-grade teacher Joya Wornson was among those who decided to stay at Groveton. First-grade classes at Groveton are capped at 18 students, compared with a cap of 25 students at most Fairfax schools, and Wornson has only 11 children in her class.

Kindergarten teacher Sueann Tupy said she feels so strongly about what Groveton is doing that she had her fifth-grade daughter transferred to the school.

"As a parent, I thought the idea of more time in class and more resources was great," Tupy said as she put the finishing touches on her classroom.

Staff writers Jay Mathews and Christina A. Samuels contributed to this report.

CAPTION: Kindergarten teacher Sueann Tupy talks with Christopher White, 5, on the first day of school at Groveton Elementary School in Fairfax County.

CAPTION: Groveton Elementary Principal Christine Lamb welcomes Armando Flores Jr., who arrived at school with his father.