Ligia Glass stood in front of the Spanish class at Prince William County's Woodbridge High School and posed the question to the students, all of whom were Latino: Why were they taking Spanish when they had grown up hearing or speaking the language?

Pedro Medina, a senior, was ready with an answer for Glass, a professor visiting the class. "It's the same as Americans who take English classes. They want to get better at English," said Pedro, 16, who spent much of his childhood in Puerto Rico. "We want to get better at Spanish."

Medina was taking a class that is the first of its kind at Woodbridge: Spanish for Native Speakers. Classes such as this one are popping up across the nation as educators conclude that children who hear and speak a language other than English at home should study that language differently from those learning it for the first time.

"To be fully bilingual, you must be able to read, write and speak the language well," said Glass, a systems analyst who is an adjunct professor of Spanish at Northern Virginia Community College. "Many of these kids can do one or two, but not all three."

Because heritage classes, as they are sometimes called, have lacked an established curriculum, the challenge of how to teach these students has been left to individual teachers.

At Seneca Valley High School in Montgomery County, Spanish teacher Carmen Morales uses an immersion approach. In one of her native-speakers classes, students ranged from fluent to barely able to compose a Spanish sentence. "Their common thread is identity," said Morales, who instructs her students with textbooks created for heritage speakers, as well as with slides and literature from their countries of origin.

In a recent class, Morales spent much of the hour speaking only Spanish about everything from the importance of eating a nutritious breakfast to preparing for the SAT exams. From time to time, she shot a question at a student -- "Why is it important to have a good breakfast?" -- and waited for the answer in Spanish.

Even Latino students who don't speak Spanish fluently said they feel more comfortable in the native-speakers class because they are not faced with other students who assume they speak Spanish.

"When I took regular Spanish, people were surprised when I didn't know what something meant," said Gaby Behzadi, whose mother is from Bolivia. Gaby, 15, said she found regular Spanish classes too easy because of the years she spent listening to her mother and grandmother chat. One in five U.S. residents speaks a language other than English at home, according to the U.S. Census Bureau. The new heritage classes are designed to build on existing skills.

Glass, one architect of heritage classes in the region, this month went to the Woodbridge class taught by Zayda McCorkle, an Ecuadorian immigrant who saw the need for such a program as the school's Latino population grew. Traditional Spanish classes for beginners were "an easy A" for Latino students, who already knew how to tell time and ask directions, McCorkle said.

The heritage classes focus on grammar, which the students often don't know because they haven't studied Spanish formally.

Cristina Gomez, 16, who came from El Salvador six years ago, speaks Spanish fluently and often serves as a translator for her family. But she said she took the class because "I want to write better. . . . I have problems with the accents. I don't know where they go."

One class exercise McCorkle devised involved writing Spanish sentences on strips of paper and ripping them in half. The students put the sentences back together by matching noun and verb. When Fernando Guillen-Garcia put two pieces together, his partner, Cindy Cruz, told him in English that the singular verb -- ha cantado, "has sung" -- didn't fit the plural noun he had placed with it. They found the right noun and continued the exercise, chattering away in both languages.

Educators say that heritage classes are a work in progress because of the range of proficiency among students. Some students can understand the language but not speak it; others can speak the language but can't read or write it. The students have been given various labels: native speakers, quasi-native speakers, residual speakers and home-background speakers.

"We haven't known as an educational system quite how to do it," said Guadalupe M. Valdes, a Stanford University professor who is known as the guru of heritage-speaking research after teaching children of Mexican immigrants in New Mexico in the 1970s.

"They were speaking a different Spanish than what was in the textbook," Valdes said. "Their Anglo-American teachers would hear Mexican Spanish or colloquial Spanish and would try to remediate it." But Valdes realized that the goal should be to enhance their current skills. Heritage students, even if they only heard the language without learning to speak it, had broader cognitive abilities than the first-time learner, educators discovered.

"The attitude has been to kill the immigrant language so we can reteach it," Valdes said. "That's just inefficient."

Another heritage instruction pioneer, Spanish linguistics professor Maria Carreira of California State University Long Beach, predicted a "paradigm shift in the way we see the teaching of foreign languages in the United States."

But Catherine Ingold, deputy director of the National Foreign Language Center at the University of Maryland, said that lack of funding has prevented educators from tracking heritage language programs across the country. Although the programs have existed since the 1970s, Ingold said they have grown significantly only in the last decade. In addition to Spanish, similar programs have been created for students of such backgrounds as Hindi, Arabic, Russian, Persian and Native American.

"These people are raw material for future competition," Ingold said. "We can invest in bilingual professionals who can help us out with the problems we are having in the rest of the world. Right now we're wasting it."