WASHINGTON — The high unemployment rate has provided an unexpected boon for the nation's public schools: legions of career-switchers eager to become teachers.

Across the country, interest in teacher preparation programs geared toward job-changers is rising sharply. Applications to a national retraining program based in 20 cities rose 30 percent this year.

In many places, there are more converts to teaching than there are jobs, except in hard-to-fill posts in science, math and special education classes. But the wave of applicants might ease teacher shortages expected to develop as 1.7 million baby boomers retire from the public schools during the next decade.

The newcomers come with a host of unknowns, including how much training they will need before they can handle a classroom full of rowdy or reluctant students and whether they are likely to stay in a profession that is struggling with low retention rates.

About one-third of new teachers graduate from 600 so-called alternative certification programs developed to bring people with no education background into classrooms. The programs vary widely, including two-year graduate degrees and online courses.

President Obama is proposing to devote more than $100 million in his 2010 budget to programs that recruit and train skilled mid-career professionals.

TRAINING RETOOLED

Some alternative programs have proven to be "excellent recruitment engines," said Sharon Robinson, president of the American Association of Colleges for Teacher Education. But training must continue to be retooled, she said, so new teachers are not put "in the deep end of the pool" right away. "It's not fair to them and certainly not fair to the students they encounter," she said.

Career-changers are considered desirable because they bring maturity and outside experiences into classrooms. They also help solve a perennial problem in public education, particularly in math and science: Too few teachers have a solid grasp of the subject they teach.

Sam Rigby, a scientist with three degrees, is among the latest recruits. The 36-year-old Washington native studied minerals in a Portland, Ore., laboratory and scoured volcanic rocks on the Pacific Ocean floor as a research scientist. This summer, after a five-week intensive course, Rigby will reinvent himself as a physical science teacher at Charles Hart Middle School, a District of Columbia school undergoing a major overhaul because of chronic low performance and discipline problems.

The educational and economic disparities in the District "always gnawed at me," Rigby said. "I thought, 'What can I do to help?' "

His $45,000 starting pay is a slight raise from his most recent job at a nonprofit agency and a bigger increase from unemployment checks he briefly received. Some of his colleagues have left much higher-paying jobs to teach.

The New Teacher Project, founded 12 years ago by Michelle Rhee, now the D.C. schools chancellor, oversees Teaching Fellows programs such as the one Rigby is in. The programs were established to eliminate the achievement gap by recruiting career-changers and college graduates to work in inner-city schools. Applications to the local program are up 80 percent over last year.

Like Teach for America, which places high-achieving college graduates in urban schools and had a 40 percent increase in applications this year, the Teaching Fellows program moves new teachers into classrooms quickly and provides mentors and training on the job.

Many reformers say a fast track is the best way to capture potential teachers. "If you get rid of the hoops and hurdles, you can get some fantastic people to come into teaching," said Michael Petrilli, vice president at the Thomas B. Fordham Institute.

Some initiatives seek to avoid traditional education school curricula completely. The American Board for Certification of Teacher Excellence approves teachers in nine states through online training and tests. The New Teacher Project has authority to certify its teachers with a practical, yearlong seminar series led by D.C. public school teachers.

DEGREES REQUIRED

Most states require education degrees for certification, but reformers say such degrees should not matter. Some studies have shown that students perform as well or better, on average, with a teacher from Teach for America or the Teaching Fellows program than they do with a traditional education school graduate.

Every minute counts for Rigby in his summer training institute, which will pay him a $2,500 stipend when he finishes. In the mornings, he teaches lessons on mitosis and the water cycle to a dozen summer school students at Cardozo High School with another fellow and a mentor teacher. In the afternoons, he joins a dozen other science teachers to learn practical teaching strategies, such as how to teach science to students who are behind in reading or math skills.

Linda Darling-Hammond, an education professor at Stanford University, said accelerated training programs that put teachers in charge of classes right away can lead to higher burnout rates because teachers become quickly overwhelmed. Her research shows that teachers with more comprehensive training are less likely to leave within a few years.

"To teach kids well, you need to diagnose how they learn" and then apply the right strategies to help them, Darling-Hammond said. "Done properly ... it's a highly skilled occupation."

One promising training model sets up schools that are similar to teaching hospitals so that student teachers can learn under a great teacher in the same classroom for a year and take coursework to help analyze what they see. Such programs, known as teacher residencies, have been established in Boston and Chicago.

The New York Teaching Fellows program began in 2000 and quickly grew. Fellows accounted for more than 30 percent of new hires four years later. Most work in the poorest schools. This year, the program received about 14,000 applications for what it anticipated would be 700 spots.