Who wants to be a teacher? A whole lot of people, a new survey finds.

If you've ever thought about ditching your current job to become a teacher, you've got plenty of company. Forty-two percent of college-educated 24- to 60-year-olds would consider teaching as a career, according to a survey out Wednesday from the Woodrow Wilson National Fellowship Foundation in Princeton, N.J.

That's good news as schools brace for a wave of baby boomers about to leave their whiteboard markers behind for good. Because of retirements, teacher turnover, and enrollment growth, schools will need to hire somewhere between 2.9 million and 5.1 million teachers between now and 2020, the Federal Reserve Bank of Chicago estimates.

Tapping the potential of mid-career professionals and older adults seeking "encore careers" isn't easy, especially given their salary expectations. But education policymakers increasingly see it as essential.

School districts "won't be able to replace half their workforce unless they change the structure … to embrace these career-changers," says Tom Carroll, president of the National Commission on Teaching and America's Future, a research and advocacy nonprofit in Washington. The changes needed, he says, include more collaborative work environments and a pay structure that credits experience in other fields and rewards job performance.

Most cite personal rewards

The new survey probed the motivations and concerns of the 42 percent identified as potential teachers from the original sample of nearly 2,300. It found that of those, nearly half would consider switching careers within five years and 3 out of 10 would find it very appealing to work with children from disadvantaged backgrounds or in a low-performing school.

The numbers are "wonderful, because those [types of schools] are where the greatest needs are," says Arthur Levine, president of the Wilson Foundation, which works to improve teacher preparation and close achievement gaps.

Most potential teachers say it's extremely important that their job be personally rewarding (68 percent). The second most common motivation: "contributing to society and making a difference" (54 percent).

Only 26 percent say salary is extremely important. But for some subgroups, that figure is much higher: 59 percent for African-Americans, 45 percent for Hispanics, and 39 percent for men ages 24 to 39. Nearly 6 in 10 potential teachers say they'd need a starting salary of $50,000 or more. The report notes that states' average starting salaries are generally under $40,000.

If teaching salaries were higher, the pool of potential career-switchers would be even larger. Of those surveyed who were not thinking of becoming teachers, 30 percent said they found the career appealing, but some aspect of teaching prevented them from seriously considering it – for 44 percent, it was low pay.

"We pay a very high price for attrition…. If we could reduce that, we could raise salaries," Mr. Levine says. "The bottom line is, if states want these people to become teachers, they will – if the states are willing to make this attractive." That would require a mix of policies, he says, to lure in, train, and mentor career-changers.

Tapping into the pool

Many alternative pathways into teaching have cropped up over the past 25 years. Nearly 20 percent of new teachers were certified through alternate routes in 2005, the US Department of Education reports.

But while 47 states have some form of alternative certification, many aren't as "alternative" as they seem, according to a study last year by the National Council on Teacher Quality, a nonprofit advocacy group in Washington.

One potential barrier for career-changers is that 32 states still require people to have majored in the subject they want to teach. "States have made the right first step in even allowing alternate routes," says Sandi Jacobs, the council's vice president for policy, "and now they have to make sure that what they have on their books is both flexible to nontraditional candidates [and] also of high standards."