These schools embody the attractive theory that we might be able to erase the achievement gaps between black and white children and between poor and middle-class children with nothing more than new and improved schools. But despite their robust test scores, there continue to be debates over whether these charter schools work for the most disadvantaged children in neighborhoods like Harlem, and no one has yet demonstrated whether the KIPP model could succeed at the scale of an entire school system.

Geoffrey Canada, the founder of the Harlem Children’s Zone, premised his organization on the idea that schools like KIPP’s, though needed, are not enough on their own. To solve the problem of academic underperformance by low-income children, he argues, we must surround great schools with an effective system of additional services for poor families.

These two strategies  call them the KIPP strategy and the Zone strategy  are not fully in opposition; they borrow ideas and tactics from each other. But they do represent distinct theories, both new, both promising and, at this point, both unproven.

So, at this moment of uncertainty and experimentation, should the federal government wait, as critics of Promise Neighborhoods suggest, until ironclad evidence for one big solution exists?

Or should it create a competitive research-and-development marketplace to make bets on innovations, the way the government did during the space race and in the early days of the Internet, and allow the most successful strategies to rise to the top? In his 2007 speech, Mr. Obama made it clear that he envisioned Promise Neighborhoods as precisely this kind of laboratory. “Every step these cities take will be evaluated,” he proposed, “and if certain plans or programs aren’t working, we will stop them and try something else.”

A certain skepticism with regard to innovation is always wise, especially in public education, where highly touted new programs often turn out to be disappointments. The problem is that for low-income and minority Americans, the status quo is a deepening calamity. The New York state test results released last month showed that the gap in reading scores between black and white elementary- and middle-school students grew from 22 percentage points in 2009 to 30 points in 2010, while the math gap grew from 17 points to 30 points.