If confidence in public schools weren't already precarious enough, it was further shaken by remarks made by U.S. Education Secretary Arne Duncan in a speech delivered at Columbia's Teachers College on Oct. 22.

Duncan urged an overhaul of schools of education, calling them cash cows that do a mediocre job of preparing their graduates for the demands of the classroom. His charges made headlines, but they were not new. They echoed many of the points made by Arthur Levine, former president of Teachers College, in "Educating School Teachers in 2006," and by David F. Labaree in "The Trouble With Ed Schools" in 2004.

In fact, the nation's 1,206 university-based education schools have long received low grades because of their lax admission and graduation standards. More than half accept virtually all applicants and require minimal evidence of competency for certification. Critics say it's no wonder their students down the line are shortchanged. If education schools were more rigorous, outcomes would dramatically improve.

At least that's the argument.

But a closer look calls into question this cause-and-effect line of thinking.

To begin with, some of the teacher-preparation programs in existence have long been top notch. Teachers College, Harvard, Stanford and UCLA are familiar brands, but lesser-known names such as Emporia State University in Kansas and Peabody College in Tennessee are close behind.

But beyond rankings, there is the more important matter of supply and demand. Can the need for quality and quantity be satisfied simultaneously?

This question lies at the heart of the issue. The numbers tell why. There are approximately 50 million students in 90,000 public schools in the United States who are taught by 3.2 million teachers. Every year, schools hire more than 200,000 new teachers for the first day of class in the fall. But by the time summer rolls around, at least 22,000 teachers have quit. Those who make it through the crucial first year, however, aren't likely to stay. About 30 percent flee after three years, and 45 percent are gone after five years.

This churn-and-burn rate not only costs public schools an estimated $7.3 billion annually, according to the National Commission on Teaching and America's Future; it also makes it extremely difficult to maintain teacher quality. The conflict between the persistent need for new teachers and the urgent need to screen for competence is given short shrift by critics.

The problem will only get worse in the next decade. Approximately 37 percent of the education work force is over age 50 and considering retirement, according to the National Education Association. As a result, the United States faces a double-whammy. Tens of thousands of new teachers will leave the profession yearly because they can't take it anymore, just as many or even more veterans are retiring. Where will qualified replacements come from?

Yet in spite of the numbers, reformers insist that schools of education are to blame for the disappointing performance of students. They assert that if schools of education were preparing teacher candidates better, once they were in the classroom they would be able to turn around failing schools.

But even the best schools of education cannot produce teachers who are miracle workers. They cannot inculcate in their candidates the wherewithal to overcome the huge deficits in socialization, motivation and intellectual development that disadvantaged students bring to the classroom through no fault of their own.

There is an enormous difference between qualified teachers and inspired teachers. What students from chaotic backgrounds need the most are the latter. But no one has ever figured out how to create virtuosos in any field. Teaching is no exception. It is more art than science. How many Frank McCourts, Pat Conroys or Jaime Escalantes exist? And how did they come to possess the talent to get the remarkable results they did with their students?

The sheer number of teachers needed to staff schools across the country should make it abundantly clear that reformers are engaged in wishful thinking. Schools of education certainly need to improve, but they don't deserve wholesale condemnation. It only serves as a distraction when so much is on the line.

But try telling that to self-styled experts who have never taught a day in public schools.

Walt Gardner taught for 28 years in the Los Angeles Unified School District and was a lecturer in the UCLA Graduate School of Education. Contact him at walt.gard@verizon.net.