Sen. John McCain has not let Sen. Barack Obama’s attack ad on education go unanswered.

And he’s hit back hard. (I’ve pasted the video below.)

The commercial slams Obama for not making a “significant mark” on education, for being “elusive” on accountability, and defending the “public school monopoly.” And then there’s the kicker: The ad says Obama’s one accomplishment is “legislation to teach comprehensive sex education to kindergartners” before they learn to read.

The ad, in effect, singles out a vote Obama cast a member of an Illinois state legislative committee, which approved a bill that would allow schools to teach sex ed to students younger than 6th grade.

And, if you caught the first two words of the commercial, you’ll see that it cites Education Week for declaring that Obama “hasn’t made a significant mark on education.” Of course, there’s more to the story than that, and you can read David Hoff’s entire piece from 2007, early in the Democratic primary race, here.

The Obama campaign, meanwhile, has decried the ad as “shameful.”