Emily Jenkins’s debut novel, Mister Posterior and the Genius Child (Berkley), has a title that screams lo and behold! Unfortunately, this title also bespeaks a self-conscious buffoonery that wrecks the emotional truth of the tale. Jenkins gets a lot right as she traces one milestone year in the life of one precocious little girl; but because it all hinges on certain events that defy belief, it feels like a sham. And that’s a shame, because Jenkins has created characters and relationships that (in isolation) resonate with sensitivity and humor.

The novel is told by a 38-year-old looking back to the year when she first became " conscious of myself as a person with secrets, as a free-thinking human being with something to say. Something not everyone wanted to hear. " In 1970 she was eight-year-old Vanessa Brick, and she was being raised by her single mom not far from Harvard Square.

Vanessa, we learn, is one of the few scholarship kids at Cambridge Harmony K through Twelve, where the teachers traipse around in braids and sandals, the kids endure a daily " Circle of Sharing, " and the regularly scheduled sing-along is called " This World Is Ours To Share. " It’s a fuzzy-wuzzy cosmos colored by endless pitter-patter about sharing and openness and individualism, even though most of the grown-ups tend toward judgment and hysteria rather than free thought. It’s a time and place choking on hypocrisy, and ridiculous enough to hint at secret perversions, and Jenkins often captures that ridiculousness. The deadpan sensibility the author has created for Vanessa would have sufficed to skewer her world. But Mister Posterior makes use of defining " Incidents " that feel like instead like calculated fibs.

The whole story is thrown into doubt from the first paragraph of chapter one: " My most vivid memory of third grade is when a child named Marie pushed me up against the wall in our classroom and showed me her ass. " This critical scene and introduces the farfetched mooning motif that runs throughout Mister Posterior. Vanessa is traumatized and stews endlessly: " Or maybe there was something particularly horrible about my own bottom, and she was waving her legitimate one at me in triumph. " What kid would have such thoughts? And what lonely third-grade newcomer would go around pulling down her pants? Mooning may have been a fad in the ’70s, but third-graders tend to be feverishly private about their bodies.

This " Incident " (one of the words in Vanessa’s Super Duper Spelling group) presages and counterpoints other bum barings that are no less ludicrous. Marie goes on to become a vivid presence in the story, but it’s hard to forget her first appearance. She’s oversized and vaguely scary - enough by itself to make Vanessa uneasy. When Vanessa embellishes the " Incident " for her friends and then realizes she’s probably ruined Marie’s chances of ever fitting in, she feels regret. But her lie also makes her feel safe and more popular, and this is why Mister Posterior is so frustrating: implausibility gives way to something genuine, over and over again.

Vanessa’s relationship with Debbie (as her mom insists she call her) is a vital piece of the story, and Jenkins captures the interplay between the smart girl and her strong mom. And her friendship with Anu, " a fast-talking Indian girl, " pulses with little-girl intensity, whether they’re playing with toy horses in the tub or chewing on clover together. Anu radiates a blanket of self-confidence that makes Vanessa feel protected.

So far, so real (except the bum). But then they have a falling out, and Anu gets mooned by a masked man in a park. She’s so utterly scarred that she turns into a fearful little wuss and is lost to Vanessa forever. At about the same time, a man starts climbing up next to Vanessa’s window and mooning her after she’s all tucked in for the night. Unlike Anu, Vanessa is charmed by the behind, and her glib, unquestioning reaction is meant as a comment on the subjectivity of experience. Unfortunately, the whole " Incident " - and the criminal court case that ensues when the guy is caught - is no more convincing than a sad nine-year-old’s yanking down her pants in a schoolroom. Various characters keep yapping about the " flasher, " implying a sexual component that doesn’t exist. Mr. Posterior would have worked better if Jenkins had found a less silly way to dig into legitimate ideas about personal transformation.