PHILADELPHIA — Barack Obama has the teachers cheering. The National Education Association is meeting here, and Obama — like the Democratic candidates who have spoken before him — is telling the crowd everything it wants to hear.

He's "committed to fixing and improving our public schools instead of abandoning them and passing out vouchers." Washington "left common sense behind when they passed No Child Left Behind." Teacher pay must be raised "across the board."

But then Obama tiptoes into the minefield of merit pay for teachers, so delicately that he does not actually utter the words "merit pay" until the question-and-answer session.

"If you excel at helping your students achieve success, your success will be valued and rewarded as well," he says — but he hastens to add that this must be done "with teachers, not imposed on them, and not based on some arbitrary test score."

This is whispering truth to power. But for the teachers, Obama's words are fingernails on a chalkboard. They fall silent, except for scattered boos, as he mentions a modest new program in Minnesota.

"If you look between the lines on the answer, it wouldn't be the answer we were looking for," says Rhonda Wesolowski, president of New Hampshire's NEA affiliate. "He's going to have to come a long way off of that position with us," says California Teachers Association Vice President Dean Vogel.

And those were the polite ones, who were otherwise impressed with Obama. "I can't imagine if he were informed he would come before 10,000 people and say what he said," says New Jersey Education Association President Joyce Powell.

But Obama, of course, knew exactly what he was doing, which is why he was so muted. Last year, in "The Audacity of Hope," Obama endorsed higher pay for teachers, with "just one catch" — they "need to become more accountable for their performance — and school districts need to have greater ability to get rid of ineffective teachers." Today, the talk is all pay, little catch, though the Obama campaign promises more details later.

Or compare and contrast Obama in October 2005 and Obama now on No Child Left Behind.

"It may not be popular to say in Democratic circles, but there were good elements to this bill — its emphasis on the achievement gap, raising standards and accountability," Obama said then. "Yes, it's a moral outrage that this administration hasn't come through with the funding. ... But to wage war against the entire law for that reason is not an education policy, and Democrats need to realize that."

Obama today acknowledges that "high standards and accountability, in the abstract, are right," then launches into the standard attack he once decried.

"Don't tell us that the only way to teach a child is to spend too much of the year preparing him to fill in a few bubbles on a standardized test," he says. But, for all the flaws of No Child Left Behind, that bubble-filling has highlighted the achievement gap between rich and poor schools, and between black and white students, and put pressure on systems to address it.

You might expect more from a candidate who sneers at "slogans without substance," as he told the delegates, and presents himself as being above tired ideological divides. Still, Obama may be what passes for brave among a fainthearted bunch. Of all the Democratic candidates who came here to pay homage to the NEA — the sole Republican was former Arkansas Gov. Mike Huckabee — Obama was the only one to deviate significantly from the union line.

Not Hillary Clinton, who tangled with the Arkansas teachers union when she oversaw education reforms that included mandatory testing for new teachers.

Not John Edwards, who bemoans the "two public school systems in America — one for the wealthy, one for everybody else," but isn't willing to acknowledge how No Child could help bridge that gap.

Not Chris Dodd, who issued a press release zinging merit pay.

There are plenty of good ideas for a Democratic candidate who doesn't mind incurring the NEA's wrath.

The Democratic-oriented Hamilton Project has proposed assessing teachers after their first two years in the classroom and weeding out those at the bottom.

Strong American Schools, a nonpartisan group that has launched a $60 million effort to bring education issues to the forefront, is pushing more rigorous education standards, more time in school for students and higher pay for better-performing teachers.

The Education Trust and the Aspen Institute have thoughtful proposals to improve No Child Left Behind, not gut it.

But so far, anyway, the Democrats who would be president are happy to propose more spending on education but are reluctant to impose any demands in return — in other words, they are happy to sound like the same old Democratic Party, permissive and beholden.

Yes, teachers are an important Democratic constituency, but aren't parents Democratic voters, too — parents who might welcome a message about accountability and expectations? If, that is, one of the candidates was willing to deliver it.

Ruth Marcus is a member of The Washington Post's editorial page staff.