The Yeows, Elizabeth and Emmanuel, both 37 and transplants from Southern California by way of the Washington suburbs, had their hearts set on a Center City lifestyle after Emmanuel, a federal employee, was transferred here last summer.

Then, Elizabeth recalled, a Philadelphia friend provided some local wisdom: "It's easier to find a good house in Philadelphia than a good school." Which sent Elizabeth, a teacher with three children, to the computer to research the Penn Alexander School in University City. Which led the Yeows from their Center City dream to a home at 45th Street and Larchwood Avenue in what has become Penn Alexander's coveted catchment area.

One more family - three more children - in University City's Spruce Hill neighborhood who would not be there if the Philadelphia School District and the University of Pennsylvania had not come together almost a decade ago to build the ultramodern K-8 school at 42d and Spruce Streets.

The school, with math and reading rankings well above the state average, has helped make the community one of the most sought-after in the city, bringing rapid change in a neighborhood that was seen as gasping for air 15 years ago.

Housing prices are up, crime is down, and amenities such as Clark Park and the popular neighborhood swimming pool have been upgraded. And there are a lot more children.

Not all of that was inspired by Penn Alexander alone. "The school is a necessary, but not sufficient, condition for a high quality of life in University City west of 40th Street," said John Puckett, a professor in Penn's Graduate School of Education who has worked with neighborhood schools and is now writing a history of Penn's expansion since World War II. He also lives in the catchment area.

For longtime neighborhood resident Barry Grossbach, a former president of the Spruce Hill Community Association, what you see that you didn't used to see "is a lot of young people not connected to the university. You see baby carriages, infants more than anything else."

Penn Alexander was the final piece of a long-term Penn undertaking initiated in 1996 by Judith Rodin, then the university's president, after Vladimir Sled, a Russian native and Penn biochemist, was murdered while walking home with his fiancée. The crime shocked the neighborhood, traumatized the campus, and led to a systematic effort that first led to safer, cleaner streets, more home ownership, and the overhaul of hundreds of unsightly and abandoned houses. It's the school, though, that has made the catchment area hot.

Penn Alexander, with an architect chosen by Penn, opened in 2001, although the $19 million building, paid for by the Philadelphia School District and constructed on a five-acre site owned by Penn, wasn't finished until 2002.

Debates about the boundaries for the catchment area were bitter, dealing as they did with two basic concerns: education and property values. Some objected to any catchment area, saying every University City child should have an equal shot at Penn Alexander through a lottery.

Melani Lamond, a longtime real estate agent in the neighborhood, remembers those outside the catchment being "worried that their neighborhoods would be destroyed. Everyone would want to move in the catchment area and that's all." That, in fact, has not happened.

Penn insisted on traditional neighborhood school boundaries, and the school district - with Penn's advice - chose a tree-lined area with many blocks of large, stately homes, and some with relatively inexpensive apartment buildings, that generally is bounded by Sansom Street on the north, 40th Street on the east, Chester and Woodland Avenues on the south, and 46th Street on the west from Sansom to Pine and 47th from Pine to Chester.

The school district then created a rigorous curriculum that is further tweaked by Penn's Graduate School of Education. Class sizes are relatively small, and Penn contributes $1,300 in extra funding per student each year, which helps give kids what they can't get in most other schools: art, music, dedicated science facilities, and more.

For the 2004-05 school year, the first year of full enrollment at Penn Alexander, the racial makeup of the school was 58.4 percent African American, 22.5 percent white, 13.2 percent Asian, and 5.8 percent Latino.

By 2008-09, when enrollment had reached 527, the demographic had changed considerably: 44.2 percent African American, 30.7 percent white, 12.9 percent Asian, and 5.3 percent Hispanic. Fewer families are fleeing when their children reach school age, and more middle-class families are buying or renting homes that landlords once rented to college students.

"The catchment area has turned it into a stable family neighborhood, with kids on almost every street," said Andrew Meloney, the West Philadelphia planner for the City Planning Commission.

From the beginning, the school was expected to have a healthy impact on property values.

A differential long existed, with homes closer to Penn, the city's largest private employer, costing more than those farther away. But the gap has widened since Penn Alexander opened, and now a house in the catchment area will cost about $100,000 more than the same house across the line, according to Kevin Gillen, vice president of Econsult, an economic-consulting firm in West Philadelphia, and an expert in the Philadelphia housing market.

Cynthia Roberts, a University City activist who heads the popular neighborhood Parent-Infant child-care and after-school center, said that her daughter was only 2 when they moved to University City in the 1980s and that there were very few other children. "If I saw someone else with a stroller two blocks away, I'd want to wave, 'Hello, hello.' "

Now, Roberts said, "it's so wonderful to be walking down the street in the morning and see all these kids and their parents walking to school."

Annie Baum-Stein, who in the fall opened Milk & Honey, the first gourmet grocery in the area, also has a child in kindergarten. "The joke among my friends is that for the first time you're seeing nannies in the neighborhood," she said.

Baum-Stein said she and her husband, Mauro Daigle, were swayed to open the store on Baltimore Avenue between 44th and 45th Streets by the idea that the growing number of young homeowners in the neighborhood needed a place to shop.

Across the street from Milk & Honey, Jon Bekken and his wife, Alexis, opened the impossibly cramped Bindlestiff Books in 2005.

One-third of its inventory is for children and young adults. "We always thought that children's books would be important," Jon Bekken said. "The school does create a population more engaged in reading and education."

Roberts feels the impact of the demographic shift at the Parent-Infant center, which is in the midst of a $1.5 million expansion partially funded by Penn. The center serves 240 children in two groups - infants to preschoolers and those up to sixth grade who come after school, and the expansion will add 50 spots.

Roberts said the waiting list for infants can reach 18 months and many are registered before they are born. "Lots of kids on our waiting list have the first name of 'Baby,' " she said.

Lee Huang, who works for an economic-consulting firm in University City, chose Penn Alexander before he had children. Huang said he and his wife moved to the neighborhood for the school, but that was 10 years ago, before it was even built, and well before their daughter, Jada, was born. "They were talking about it then and we thought, 'That's a good thing.' We didn't know how good it was going to be. And, God willing, this is where she will be going next fall."

Which is why he arrived at Penn Alexander's front entrance a few minutes after 7 a.m. on the last Wednesday in January. It was 30 degrees and raw, and, like the six other parents there, he was dressed to withstand the frost. It was the day to enroll children in next year's kindergarten class, and, though registration didn't begin until 8:30, Huang and the others had arrived early to beat the competition.

There are about 50 kindergarten slots at Penn Alexander. Acceptance, unnervingly, is first come, first served.

What Huang and his colleagues didn't know was that they were already dangerously close to the bubble. About 45 parents, some arriving well before 6 a.m., had been given numbers earlier by principal Sheila Sydnor to verify their place in line. She told them to go home, warm up, and return at 8:30. Huang, who eventually received number 53, was told he would hear in about six weeks whether Jada had been accepted.

He got the word two weeks ago.

"She got in," he said happily. "I was holding my breath. I was a little nervous."