Ben Taplin and Nate Nisenson have been best friends for half their lives. They started kindergarten together at Long Branch Elementary School, and now, as third-graders, they sit together on the school bus, trade Yu-Gi-Oh cards and spend hours playing Spy Club, a game they made up.

Ben's little brother, Sam, a kindergartener at Long Branch, has a best friend there, too, named Tom, and Sam and Tom's toddler sisters look poised to continue the best-friend tradition.

So when the Arlington County school system posted four scenarios on its Web site last month that showed potential new attendance boundaries for up to 11 North Arlington elementary schools, Ben's family was alarmed. New attendance zones might mean the friends would be separated.

"It would be very upsetting," said Kathy Kavalec, Ben and Sam's mother. "Nate's been Ben's closest friend and the one he's most comfortable with. And Sam was scared to go to kindergarten, and one of the things that got him through was that Tom was in the class with him."

School officials say that recent demographic shifts have caused an imbalance in enrollment, leaving some schools crowded and others underused. The plans posted on the Web site showed variations of what redistricting -- which would even out enrollment by moving children between schools -- might look like. In two of them, Ben and Sam would be among several hundred students moved -- in their case, from Long Branch to Barrett Elementary School.

School boundary changes are never easy. Parents are reluctant to remove their children from schools they like and where they know the teachers and staff. They worry about separating their children from friends and sending them to unfamiliar schools. South Arlington schools went through a similar process two years ago, causing consternation among parents. Boundaries were last redrawn in North Arlington 10 years ago.

School officials say one of the reasons Arlington schools tend to become crowded more quickly is the district's small classes -- about 22 students per class. The Arlington School Board began discussing possible boundary changes last December, but the controversy started when the scenarios were posted on the Web site. They showed that the following elementary schools could be affected: Ashlawn, Barrett, Glebe, Jamestown, Key, Long Branch, McKinley, Nottingham, Taylor, Tuckahoe and Arlington Science Focus.

School officials say the scenarios were never anything more than examples of what redistricting might look like and were not meant to be taken literally. School Board Chair Libby Garvey said that posting the scenarios was meant to provide transparency about the decision process.

"We thought the worst thing in the world is to have these quote-unquote 'secret' maps, so we put them up on the Web," she said.

The district abruptly removed the scenarios from its Web site a few weeks later, after an avalanche of angry feedback from parents in the affected neighborhoods.

"They caused more confusion than they were worth," said Meg Tuccillo, director of administrative services at Arlington public schools. "So rather than continue this anxiety and unhelpfulness and thinking that these were done deals, they were taken down."

But the damage was done. Worried parents have circulated petitions, exchanged angry e-mails and packed School Board meetings to give emotional testimony about the impact boundary changes would have on their children, and to plead with the board to find other options. They contend the boundary changes would also mean that some children would have to cross busy thoroughfares to get to school, and in the end they say the changes might not even solve the enrollment problems.

In recent weeks parents have been meeting with board members individually to air their feelings and candidates challenging current board members in the Nov. 2 election have made their opposition to the boundary changes central tenets of their campaigns.

"All the scenarios would take [my daughter] away from her friends and her community," Maria DiGiulian, a Long Branch parent, said at a recent board meeting.

"We're not just a bunch of numbers on a map to be divided up," said Lisa Stern, the mother of a fourth-grader and a second-grader at Tuckahoe, which could lose some students to Glebe.

"Dividing this neighborhood is simply unacceptable," Jennifer Dunlap, president of the Long Branch PTA, said. "This isn't messing with a couple of streets. This would be taking half the school and ripping them away."

Last month, a 45-member boundary committee made up of parents, teachers and principals from each affected school was formed to study the issue. The committee is scheduled to make recommendations to Superintendent Robert G. Smith by early December; he is scheduled to give his own recommendation later that month. The School Board will vote on a final plan in January.

Opponents of the redistricting argue that the school system hasn't exhausted other possibilities, such as granting fewer transfer requests, or finding room in underused schools for special education programs, which sometimes devote an entire classroom to a small group of students. Some say it is not clear that the schools in question are really overenrolled and both sides say there are various ways to interpret the numbers.

In response to the parent complaints, the boundary committee last week posted a list of guiding principles for the process that include pursuing non-boundary options first and recommending boundary changes only as a last resort. The committee is awaiting new enrollment projections, which are due out tomorrow, before making recommendations.

But committee chairman Linda Henderson conceded that while the committee had not endorsed any scenario, "there is still a possibility they could be considered."

And Garvey said non-boundary alternatives, such as denying transfer requests, are problematic, too, especially in a district that allows children to opt into schools outside their home area if the schools better meet their needs.

"I would be somewhat loath to say, 'No transfers, you have to go to your neighborhood school,' " Garvey said. As for moving special education classes, she said, the school system has made keeping those students in their neighborhood schools a priority.

Garvey said one solution might be to "team," or overlap, several school zones to allow children to have more than one home school.

"How reasonable it is, I don't know," she said, acknowledging that parents may simply choose to stay with their current schools.

The fears have trickled down to first-graders such as Hayley Roy, a Long Branch student who heard the news from her best friend and lemonade-stand partner Sophia Hays. "Last week she came home and said, 'Sophia says she's going to have to go to a new school,' and we were both so sad," said Hayley's mother, Natalie Roy. "It doesn't make any sense to us why they'd even think about doing this."

Underneath the concerns about separating friends and children crossing busy streets lie more prickly issues of race, socioeconomics and test scores. Each boundary scenario included the transfer of some students from high-performing schools whose students tend to come from wealthier homes to schools with lower test scores and more students who come from poor homes or have limited English skills.

For example, about 72 percent of Barrett students receive free or reduced-price lunches, an indicator of poverty, compared with 35 percent of students at Long Branch and Glebe and 4.5 percent at Tuckahoe. Barrett's student population is 67 percent Hispanic, a large number of whom do not speak English as their first language. In addition, Barrett was one of six county schools -- the only one in North Arlington -- that failed to meet annual benchmarks under the federal No Child Left Behind Act and had to offer parents the option of transferring their children out of the school this year.

But Anne Steen, a former Barrett PTA president, kept her children in Barrett even after moving two years ago to a house near Nottingham Elementary School.

"We have nothing against Nottingham, but at Barrett they were getting a great education," Steen said. "The science and math focus at Barrett were very important for both of my kids." She added that at Barrett, the test scores of native English speakers from wealthier families are comparable to scores of similar children in other county schools. She also noted that Barrett's principal won the county's Principal of the Year award three years ago and that one of its science and math teachers won Virginia's Teacher of the Year award this year.

Opponents of boundary changes say they are committed to diversity and that their objections have nothing to do with socioeconomics or race. In fact, some parents at Tuckahoe, which is 86 percent white, say the boundary scenarios, which would move some of its students to the neighboring Glebe, could leave their school less diverse, which parents point out goes against the district's and the boundary committee's stated intent.

But others contend the parents are indeed reluctant to transfer their children into a school with a high level of racial and socioeconomic diversity.

"It makes people uncomfortable," said Kathy Rehill, a mother of two young children who attend Glebe, which is 34 percent white. Glebe, whose Standards of Learning scores are lower than Tuckahoe's, is operating at 71 percent of its capacity. Thirty-five percent of students who live in the Glebe attendance area attend other schools, compared with the 27 percent districtwide average for elementary schools, according to school system data.

"People in Arlington want a little bit of diversity, but not too much," Rehill said, adding that she wishes people would give Glebe a chance.

"It has beautiful new buildings, a new principal and great teachers," she said. "I just would like to see people not be so misinformed about a school based on stereotypes."

Real estate also plays a role. Mary Jane Hickey, a mother of two, said she and her husband liked Tuckahoe school so much that three years ago they extensively remodeled their house rather than move out of the area, only to learn that her children, now 5 and 3, may be redirected to Glebe.

Troy Schneider said he and his wife bought their house in part because it was in the Tuckahoe attendance area. He said he worries about sending his son Mateo, now 1, to a school with lower test scores, but added that his objections run deeper; he questions the whole logic behind redistricting.

"Glebe is very much under capacity right now," he said. "So one would assume that Arlington wants to make all of their schools as good as they can possibly be. So let's assume that two, three, four years from now Glebe is a better school, the parents are more involved."

At that point, he said, so many parents might send their children there that it would become overcrowded and could necessitate further redistricting. "It seems like a self-defeating situation."

But school officials say the South Arlington redistricting was successful in evening out enrollment and that as older children move on, young couples move into neighborhoods and additional housing is constructed, such adjustments are sometimes necessary. "It's a cyclical kind of thing," Garvey said.

Rehill said she sympathizes with parents who bought houses based on the current boundaries. "Everybody's got their heels dug in because they bought houses based on that," she said.

But, she added, "Somebody's always going to have to be on a border."

Mary Jane Hickey, top, and her husband, Houman Jalali, and their children Brendan, 3, and Kiara, 5, worry about the possible changes in school boundaries. Troy Schneider, left, hopes that his 14-month-old son, Mateo, will be able to go to school at Tuckahoe Elementary, but under the potential redrawing, he might attend Glebe Elementary.Deena Ackerman of Arlington speaks up at a recent School Board forum at Long Branch Elementary.Long Branch's Hayley Roy would no longer attend school with one of her best friends under one boundary scenario.