I laughed quite a few times in Juno. Diablo Cody can write a swell joke... but a full screenplay? She's not there yet. Juno is more a piecemeal bucket of clever set-ups than a true film about a pregnant 10th grader. The only high school insight we get is when Juno tells us how jocks quietly pine to pork nerdy "McSweeney girls" and that cheerleaders secretly get wet for Woody Allen quoting English teachers. (Indeed, right now, Cody stands as nothing more than an underdeveloped Woody wannabe, herself,... but for the YouTube generation.)
From there we jump to bizarre Dario Argento, Herschell Gordon Lewis, Mott the Hoople, and Patti Smith references but their context is scattered. It's empty posturing, nifty name-dropping. Diablo Cody wants to share her pop-culture preferences and sensibilities than that of a modern day teenager. Amy Heckerling and John Hughes understood that folly, and made it task numeber one to observe the younger generation before making Fast Times at Ridgemont High, Clueless, Pretty In Pink, and The Breakfast Club (all superior screenplays to Juno's).
Even other-worldly teen films like Rushmore - with it's mythical portrayal of teen ambition -, or Brick - with it's playful goof on high school drama playing out like the dark tensions of a film noir -, gave keener demonstrations of postpubescent life. But Cody isn't a total wash. She's definitely got something. In Juno's best set-up, Juno treks some living room furniture over to the front lawn of her boyfriend Paulie's house. The next morning she greets him in a laz-e-boy, rug at her feet, pipe in her mouth, and tells him the pregnant truth. It's a moment of adult future and responsibility meeting an unexpecting teen at the door, yet this type of braininess sadly ran dry for the rest of the film.