At Mosby Woods Elementary School in Fairfax County, an art coach from the Kennedy Center helped children play historic figures in a living museum. The fourth-grade class went on a trip to Jamestown. And this summer, the school's library will be open a few hours each week so children can check out books without leaving the neighborhood.

Principal Mahri Aste said those programs have helped boost student performance. But next year, less federal funding will be coming in because the school is becoming, at least on paper, less poor. And Aste worries that if the trend continues, some programs could be cut.

The problem, Aste said, is that the school has to educate the same number of students who are extremely poor. The on-paper change started in 2003, when Mosby Woods became home to a center for gifted students -- students from Mosby Woods and four nearby schools in middle-class or even affluent neighborhoods. The influx of wealthier students skewed the reality, Aste said.

"The number of children in poverty hasn't changed," Aste said. "Those kids [the gifted students] are pulled from neighborhoods other than our own, and they are lowering our overall poverty rate. As the center expands, I anticipate more cuts in our resources."

The situation at Mosby Woods, just south of Interstate 66 near Fairfax City, reflects the changing demographics of Fairfax, where pockets of poverty exist even in areas that are generally more affluent. The school, which has about 550 students, is near a large apartment complex that is home to many low-income families, including immigrants from Somalia, Sudan and El Salvador, Aste said. But neighborhoods with single-family homes surround the school.

School officials say the shift at Mosby Woods is unique in Fairfax, because the county's other gifted centers draw children from schools in neighborhoods with similar socioeconomic conditions.

Federal Title 1 funding, intended to offset the effect of poverty on education, is doled out to schools based on the number of children eligible for free and reduced-price lunches. Schools at which 40 percent or more of the children are poor receive the largest sums, and principals have more flexibility in spending, said Sue Fidelman, Title 1 coordinator for Fairfax County schools.

Fidelman said Mosby Woods is taking a hit because the percentage dropped to 39 percent. If the children in the gifted center are not included, Aste said, about 45 percent of the students are poor.

In the school year that ended in June, Aste used federal funds to hire three extra teachers and had about $17,000 left over to pay for supplies and programs. Beginning in September, the funds will cover two teaching positions, and there will be a little less for extras.

Fairfax school officials have agreed to make up the difference in funding for next year. But Aste and parents say they are concerned about the future.

The gifted center started in 2003 with a third-grade class. An additional grade was added last year. Beginning in September, the center will have third- through fifth-grade classes, and the next year, it will include a sixth-grade class.

"It's the law of unintended consequences," said Linda Ferri, the Mosby Woods PTA president. "The most at-risk kids . . . will have resources removed because suddenly there is an influx of higher-income kids."

Bill Brennan, an economics consultant who lives within the Mosby Woods boundary and has two children at the school, including a daughter in the gifted center, said even though he thinks the center is good for the school, he would rather see it move if having it stay means fewer resources for all the children.

"It just doesn't seem fair," Brennan said. "I love having the center here. But to be quite honest, I would rather have it at another school because . . . I'm worried about the kids who don't speak English and whose parents are working two jobs."