Karen Mazzotta wasted no time on a recent morning, quizzing a dozen students at Pittsburgh Minadeo PreK-5 in Squirrel Hill about the calendar, the weather and the letter of the day.

She had the children scour the room for words beginning with "Q," then count and pronounce them.

"Who always hangs out with the letter 'Q'?" she asked, hinting, "It's a vowel. They're like best friends."

Having made her point about the "qu" duo, Ms. Mazzotta pressed on.

If she moves quickly, the students don't seem to mind. They have some catching up to do.

Ms. Mazzotta is one of 14 Pittsburgh Public Schools teachers who work exclusively with students learning English as a second language (ESL), a small if quickly growing group of students here.

For years, Pittsburgh has been an anomaly among urban districts because of its low number of ESL students. While districts in Texas, Florida and California have swelled with immigrants, Pittsburgh enrolled only 273 ESL students in 2004-05.

A sluggish job market may have been responsible for the low numbers, Tim McKay, the ESL curriculum supervisor, speculated. Now, affordable housing and immigrants' family networks may be fueling an increase.

The number of ESL students jumped to 485 this school year and is projected to reach 1,085 by 2010-11.

While those remain comparatively small numbers, the increase brings logistical challenges, such as the scramble to find translators to help with 30 students from Myanmar who arrived after Aug. 1. The district previously had no students from Myanmar, and the language isn't widely spoken in Pittsburgh.

Because ESL students must take standardized math and reading tests, the growth could at some point further complicate the troubled district's efforts to comply with the federal No Child Left Behind Act.

The Los Angeles Unified School District's 266,000 ESL students, mostly Spanish speakers, represent 38 percent of the district's enrollment in kindergarten through grade 12. Henry L. Vidrio, interim director of the district's Language Acquisitions Branch, said a low graduation rate and high numbers of ESL and special-needs students are key reasons the district consistently falls short of federal achievement benchmarks.

Mr. McKay called the influx here a "good challenge."

Minadeo's 50 or so ESL students study science, social studies and other subjects with native speakers. When their peers have English class, the ESL students come to Ms. Mazzotta's room for theirs.

"What is today?" Ms. Mazzotta began one day last month.

"Today is Wednesday," Tomoki Onuma, a kindergarten student, said.

The class repeated, "Today is Wednesday."

"If today is Wednesday, what was yesterday?" Ms. Mazzotta asked.

"Tuesday," Maria Echeverri, another kindergarten student, said.

Off to one side, unfazed by the banter, a trio of more advanced students reads aloud to David Kanamugire, one of the district's seven ESL paraprofessionals. Two other students worked by themselves.

Unlike a regular English class, Ms. Mazzotta may have students in kindergarten through fifth grade in the same room. With some students, Mr. McKay said, "we have to start at the beginning."

Minadeo's ESL students represent the district's traditional population of English-language learners, mainly Asian and Arabic students whose parents have come to Pittsburgh to work or study at the universities and hospitals.

But the population has been shifting in recent years with an influx of Spanish-speakers and refugees, including the Myanmar students and the Somali Bantu children who enrolled about four years ago.

The district's 115 Spanish-speakers are now the largest group of ESL students. Pittsburgh Beechwood PreK-5 in Beechview has 47 Hispanic students, accounting for more than 11 percent of the school's enrollment.

The new groups have different needs than the traditional ESL students, and the district has faced a learning curve.

In May 2005, the Education Law Center filed a complaint with the U.S. Education Department, alleging the school district unfairly segregated more than 50 Somali Bantu students and failed to communicate with the students and their families in a language they understood. The parties reached a settlement the following year.

"I actually think the Somali Bantu kids paved the way for these other students," Nancy Hubley, the law center's Pittsburgh director, said.

Catholic Charities in Pittsburgh is preparing to settle 170 more refugees this year, including some from Nepal, John Miller, the group's refugee services director, said. It's too soon to say how many will enroll in city schools, he said.

The district next school year plans to open two "regional ESL centers" for high school students, placing 64 students at Pittsburgh Allderdice High School in Squirrel Hill and 39 at Pittsburgh Brashear High School in Beechview.

Mr. McKay told the school board last month that the change will better serve an ESL population that's becoming more diverse and geographically dispersed. Currently, all ESL students in grades nine through 12 are educated at Pittsburgh Schenley High School, an Oakland building to be closed permanently or for renovations at the end of the school year.

English-language learners constitute a "subgroup" whose performance helps determine whether a district makes federal achievement targets under the No Child Left Behind Act. The law's requirements for ESL students -- scores are counted beginning with their second year in an American school -- are widely criticized by urban districts.

The Pittsburgh district has missed federal benchmarks for six consecutive years, largely because of poor performance by black students and poor students. A growing ESL population could pose another hurdle.

The district's ESL students in grades three through five met the achievement benchmark on the state math test last year, but missed the target in reading. In other grades that were tested, the district did not enroll enough ESL students to meet the threshold for a subgroup.

English performance isn't the only consideration, however.

As they adjust to new homes, ESL students should be encouraged to retain their native language, said Mariana Achugar, assistant professor of Hispanic studies and second language acquisition at Carnegie Mellon University. Research suggests that bilingual students have cognitive advantages, and the nation has economic reasons for promoting bilingualism, she said.