Emma Stone finally gets the breakthrough role her fans have been waiting for in “Easy A.” This is the moment that takes her into the front rank of movie stars, sub-category: America’s sweetheart.

Stone has an immediately appealing presence on screen, unpretentious but utterly charming. Here she plays Olive, a girl who doesn’t yet realize that all of the things that make her feel invisible in high school are going to make her wildly beloved for decades after. She is impatient to be “interesting” and so after a thrill-less weekend highlighted by singing along to a greeting card she impulsively tells her best friend Rhiannon (Alyson Michalka) that she had sex with her college student boyfriend. Problem #1: the sex and the boyfriend are both imaginary. This is the kind of mistake a teenager would make. Problem #2: this confession occurs in the ladies’ room at the high school, with no checking the stalls. This is not the kind of mistake anyone would make after 7th grade, but we have to kick that plot into gear, now, don’t we?

And so the whole school immediately knows and believes this scandalous news. Which is why Olive’s closeted gay friend tired of getting picked on comes to her with a proposition. Not that kind. He wants her to have noisy public pretend sex with him so that he can be definitively proven manly. And since her reputation is already shot, what can it hurt? And why not do the same favor for some other needy souls? And then, when it seems the whole school is judging her (conveniently, her class is reading The Scarlet Letter), she decides to sew a big red A on a bustier and see what it feels like to go from invisible to un-missable.

Stone is such an effortless charmer that she keeps the story aloft, even when Olive inexplicably turns her little adventure into a for-pay enterprise, insisting on gift cards(!) in exchange for making the reputation of the guys involved at the cost of her own. A side story involving Olive’s favorite teacher (Thomas Hayden Church) and his wife, the school guidance counselor (Lisa Kudrow) is also unnecessarily tawdry. Far better are the encounters with the always delectable (and just about always underused) Amanda Bynes as the school holier-than-thou abstinence proponent and the always ultra-watchable Stanley Tucci and Patricia Clarkson as Olive’s deliciously off-kilter parents. Their scenes are warm, witty, and surprising, and livelier than Olive’s romantic ups and downs. In every way, it is Stone who is the heart of this movie, and she wins our hearts as well.