American schools are suffering from a chronic teacher retention crisis, with almost one-third quitting the profession after just three years, according to a new report.
Close to 50 per cent leave after five years, contributing to a high turnover rate that is undermining children's education, says the National Commission on Teaching and America's Future.
"The problem is critical," said the organisation's executive director Tom Carroll.
"The conventional wisdom is that we don't have enough teachers, but the problem is that we can't keep them. We have a bucket with a huge hole in it and the more teachers you pour in, the more fall through the bottom," he said.
In its report, No Dream Denied: A Pledge to America's Children, the commission concludes that the problem is particularly severe in urban, low-income communities and rural areas, where there is a higher concentration of new teachers. The result, it suggests, is that many feel "lost at sea", while those with more experience are thinly-stretched and over-burdened.
"We have a sink-or-swim approach in which we throw novice teachers into very challenging settings and they are not given the support they need to succeed," said Mr Carroll.
More than 250,000 teachers stop teaching every year and a further 250,000 move posts.
Those leaving for reasons other than retirement outnumber those retiring by a proportion of almost three to one.
The report calls for a national effort to improve teacher retention by 50 per cent by 2006, suggesting strong mentoring opportunities for new teachers and better training as two strategies for improvement.
It says the target laid down by President George W Bush's No Child Left Behind Act for every teacher to be "highly qualified" by the school year 20056 is in jeopardy because of the exodus rate.
James Hunt, chairman of the commission, said: "It is time for our leaders to redouble their efforts to achieve far-reaching education reform by pledging to recruit, prepare, support and pay for quality teachers."
Cuts in the number of visas that allow foreign education specialists to work in American schools could cause more problems. This year 195,000 temporary employment visas were issued to education, health and IT professionals. The number has been cut to 65,000 next year because of the number of jobs in the hi-tech sector being lost to foreigners.
The restriction could cause a greater scramble in the education sector for those that are left. Holders may work in the United States for three years, then renew for another three. At least 10,000 of America's teachers are employed on the visas.
Teri Lyons, head of teacher placement for the Los Angeles unified school district, which hired 50 foreign teachers with these visas this year, said the cuts will cause the district "tremendous problems".
The National Education Association said other types of visa are available, though they are valid for shorter periods. However, it acknowledged in June that shortages in maths, science, foreign languages and special education teachers and in staff willing to work in urban schools had helped create a global market for teachers who were plugging the gaps as temporary employees.