A growing number of school districts are hiring teachers from foreign countries to fill shortages in math, science and special education.

The trend is most evident in poor urban and rural districts, according to educators. Segun Eubanks, director of teacher quality at the National Education Association, the United States' largest teachers union, says many of those districts have trouble keeping teachers for reasons including low pay, disruptive students and a lack of books and materials.

"American workers are not willing to do the work for the conditions and pay we offer," he says. "So we're recruiting them for the same reasons we recruit farm workers and day laborers."

The National Council on Teacher Quality, a think tank, says a new teacher is generally paid $30,000 to $45,000.

The U.S. Department of Education does not track foreign teachers. The American Federation of Teachers union estimates at least 18,000 of the nation's 3.7 million teachers were hired elsewhere.

Kate Walsh, NCTQ president and a member of the Maryland State Board of Education, says it has become more common to hire overseas. "All poor districts have a harder time recruiting," she says. "Anytime you're teaching poor kids in the inner city, it's very hard to get teachers to stay."

Walsh says foreign teachers can enrich students' education by exposing them to other cultures. Eubanks agrees but says the United States must address the underlying shortage by training more teachers and improving schools.

Foreign teachers must pass state tests and meet federal requirements. Around the country: