Besides a beautiful swing-state setting, Denver once offered a subtler virtue for the Democratic Party's convention: a school system where, just as Barack Obama urges, management and labor agreed on a new way to pay teachers. Under the program known as "ProComp," Denver teachers can earn more for teaching in poorer schools and shortage subjects and for getting better results.

Approved with support from 59% of teachers in 2004, ProComp has now hit a rough patch. The current teachers' contract is expiring, and the district and union are at odds about how to change it. The union's newspaper headlined a possible strike during the convention. Senator Obama used to talk about ProComp, but doesn't anymore.

Much as Senator Obama has brought a new generation into politics, Denver's 43 year-old superintendent, Michael Bennet, is trying to bring a new generation into teaching. School leaders nationwide are watching to see whether he succeeds.

Like many districts, Denver struggles to retain talented young teachers partly because high pay is reserved for the end of long careers.

Salaries start low, around $36,000, and increase slowly, usually less than $1,000 a year. Even with ProComp, bonuses based on performance are just $1,000 annually. Then, at age 55, and sometimes a few years earlier, teachers can retire with a pension of more than $50,000 a year.

The city ends up paying at least $140,000 a year for teachers as they near retirement, and many teachers earn more after retiring than while teaching. This pattern isn't unusual nationally. Late-career salary hikes often exacerbate the backloading.

For years, the conventional wisdom in education was to focus on retaining as many teachers as long as possible. The current pay schedule makes some sense if that's your goal. But recent evidence points in a different direction. Teachers usually improve a lot in their first year on the job, then grow modestly for the next two to four years. After that, classroom effectiveness tends to plateau. What's more, at any given level of experience, the variation among teachers is enormous.

Sophomore teachers often outperform long-term veterans. Yet the young stars are often the first to leave the field.

If our focus is what's best for students, we want to limit the number of teachers at the very beginning of their careers, but it isn't critical to retain everyone as long as possible. Interestingly, the highest performing public schools, for instance the KIPP academies, don't hire many first-year teachers, but also rarely employ teachers with long experience in the classroom. Instead of trying to keep everyone, a more promising approach is to make teaching more appealing for a new generation of potential great teachers, retain the successful ones, and improve less effective teachers or help them into other careers.

With this understanding, offering big payoffs only after many years in the classroom doesn't make much sense. Young people naturally focus on the short term. As shown by Teach for America, a national program that recruits outstanding recent graduates and keeps most of them in education, many twentysomethings may be eager to teach for five or ten years, but not twenty or thirty. For them, a big pension in a quarter century isn't much of a draw.

Bennet's proposals appear to be crafted with these realities in mind. He wants to increase not only performance bonuses, but also starting salaries and annual pay hikes in the first few years. Compared to the union's emphasis on across-the-board raises, this would mean lower pay hikes in later years--and, given how pensions work, smaller increases in pensions.

Bennet's approach may or may not be exactly right, but it's a promising direction to go. Yet it also exposes a generational divide. Younger teachers not only have more to gain from the new approach, but they are also more likely to support pay linked to performance. According to an Education Sector survey, more than two-thirds of new teachers nationwide would support higher pay for teachers who get great evaluations from principals, for example, while barely half of veterans feel that way.

Barack Obama won the Democratic primary in part because he brought many young people into politics for the first time. A generation of aspiring teachers might quickly support Bennet's proposals, but they don't have a say on the teachers contract.

All of us, though, have a stake in who is teaching our children, now and in the future. Finding new ways to attract and retain great teachers is a challenge for Bennet and Obama, for Denver and the nation.