Updated Sept. 4, 9 p.m.

The core value of fact-checking is neutrality. No slant, no biases are allowed — just the recitation of a claim, an investigation of the evidence to support it and a true-or-false ruling.

And if the ever-expanding fact-checking industry is doing its collective job, then we should expect to find absolutely no disagreement from checkers on anything. Never. They must always reach the same conclusions and any deviations from this universal imperative must be highlighted and audited.

For that reason, we bring you two fact-checks of a recent campaign ad for President Obama. Here’s the ad.

The ad sets out to depict Mitt Romney as a guy who doesn’t support what’s best for parents and their children, pointedly with regard to his position on class sizes. After a father attests to the great experiences that his children have had in small classrooms, a narrator jumps in with this claim:

“But Mitt Romney says class sizes don’t matter.”

Both CNN and PolitiFact decided to zero in on that claim by the Obama campaign. Did the campaign twist and contort Romney’s alleged statement that class sizes don’t matter? Or did it accurately represent what Romney said?

CNN: “Given the facts, we are tempted to give Obama’s ad an ‘F’ for false. But we’ll settle on an ‘M’ for misleading.”

PolitiFact: “We rate the claim True.”

How could these two outfits look at the same set of facts and reach such conflicting conclusions? Uh, they didn’t, in fact, look at the same set of facts.

For its finding that the ad was deceptive, CNN relied on these two paragraphs:

Talking to a group of Philadelphia teachers in May, Romney said, “If you had a class size of five, that would be terrific. If you have a class size of 50, that would be impossible.”

But Romney cited a McKinsey Global Institute study that showed sometimes, schools with small classes fail, and sometimes, schools with big classes succeed. Therefore, he said, class size should not be given excessive weight in efforts to improve schools.

And for its finding that the ad was true, PolitiFact relied on 10 paragraphs of research, such that excerpting it right here could run the Erik Wemple Blog into trouble with copyright law. A fair abridgement, though, goes like this: PolitiFact analyzed the Philadelphia material and the McKinsey study, plus comments Romney made in Florida, plus page 216 of his book, No Apology, in which he writes that “the effort to reduce classroom size may actually hurt education more than it helps.” One of the statements cited by PolitiFact is this one: “Massachusetts data ‘showed that classroom size was not relevant in my state to how well the kids were doing.’”

Be it resolved: That the CNN fact-checking crew undergo training at the offices of PolitiFact, effective immediately. Indeed there’s some room for interpretation of Romney’s remarks given the various statements he’s made. Yet there appears to be plenty of support for the claim in the ad.

CNN responds: Tom Foreman, co-author of the CNN piece, called to explain the rationale behind the ruling. “The reason we call this misleading instead of false is because Romney clearly downplays the importance of class size. He sees it as one element of quality of education, not the greatest element,” says Foreman, who says that he had to spit out “everything we know in a couple of graphs. As we move more toward doing full Web pieces, we’ll be showing more of what we have,” he said. .