On the air and on the stump today, President Obama attacked GOP rival Mitt Romney for not embracing the idea that smaller class sizes for public school students should be a top education priority.

"When a teacher in West Philadelphia…told Governor Romney that having too many kids in his class made it harder for him to do his job, Governor Romney told him that class sizes don't matter," Obama said today in Las Vegas.

"There are a lot of studies that say that class sizes do matter, especially in the early grades," he said. "Would any parent want their kids to go to a school with much bigger class sizes?"

A new Obama campaign TV ad makes the same point, portraying Romney as out of touch.

While Romney has indeed argued that small class sizes are not the key to improving student performance, left unmentioned is that Obama Education Secretary Arne Duncan has publicly expressed a similar view.

During one meeting with education reporters last year, Duncan reportedly "firmly pushed back against reflexive small-class mania," wrote Education Week's Rick Hess, who was there.

"He said, 'Class size has been a sacred cow and I think we need to take it on. Give me and my wife a choice of putting our kids with a great teacher of 28 or a mediocre teacher of 23, and I know what I'd choose every time,'" Hess recounts.

"When pressed on the 'don't parents prefer smaller classes?' question, Duncan said, 'I don't think parents have been given the choice I just put on the table…There's no right choice there… [but] selectively raising class size' is different from simple-minded calls for bigger classes," according to Hess.

Other reports from Education Week show that Duncan expressed similar views even earlier in the administration, during a 2010 forum at the American Enterprise Institute.

"He urged districts to consider 'modest but smartly targeted increases in class size,'" reported Alyson Klein, who attended the November 2010 gathering. "As a parent, Duncan said, he'd much rather have his kids in a class of 26 with a really excellent teacher, than in a class with 22 kids, lead by a mediocre teacher."

The Romney campaign said Obama's attacks are "misleading and hypocritical" in light of Duncan's comments.

"President Obama's latest ad puts him directly at odds with his own education secretary, who has promoted teacher quality - not class size - as the most important factor in a good education," said Romney spokeswoman Amanda Henneberg.

Education Department spokesman Justin Hamilton dismissed any hypocrisy, stressing that there remains a stark contrast between the candidates on education policy.

"Secretary Duncan has said that class-size efforts should be targeted where the evidence shows they're most effective, especially the early years," said Hamilton, "And that the most important thing we can do is have a great teacher in every classroom."

"That's a far cry from that saying class sizes don't matter or that we don't need more teachers as an excuse to slash investments in education and shower tax benefits on millionaires and billionaires as the House Republican budget does," he said.