Demure farce and smart, almost scholarly comedy are the order of the day in “Tadpole,” one of the more delightfully entertaining films to emerge from this year’s Sundance Film Festival.

The title character — though no one calls him that anymore — is Oscar Grubman (Aaron Stanford), a very intelligent 15-year-old who speaks French, reads Voltaire, and is bored with the immature, thoughtless girls at the fancy-pants boarding school he attends. His best friend (Robert Iler) remarks that Oscar is a 40-year-old in a 15-year-old’s body.

While home in Manhattan for Thanksgiving, Oscar decides to profess his love for the woman he really wants: Eve (Sigourney Weaver), who happens to be his stepmother.

She is a biologist; his father Stanley (John Ritter) is a history professor at Columbia. They are wealthy and erudite, and so are their friends. High class, however, doesn’t stop Eve’s best friend Diane (Bebe Neuwirth) from seducing Oscar: That’s right, they sleep together. Only 10 years ago, such a development in a film probably would have caused more uproar than it does now. It helps that in this case, it’s handled tastefully and comically, and the point is made that Oscar is far more mature than most boys his age. (The legalities of such a coupling are not addressed, which is probably for the best in escapist fare such as this.)

There is a fantastic scene in a restaurant where Oscar pines for Eve, Diane looks for an excuse to spill what happened, and Stanley and Eve have no idea what’s going on. John Ritter is no stranger to farce, and the way he behaves here shows remarkable restraint and timing. Bebe Neuwirth, for her part, very nearly steals the show as a worldly, sassy-mouthed middle-aged vixen.

Newcomer Aaron Stanford is quite a find as Oscar. His character is a few degrees this side of Max Fisher, the protagonist of “Rushmore,” and Stanford plays him with realistic teen-age confusion. Sigourney Weaver, resplendent and graceful as ever, is a sight for sore eyes, particularly when those eyes are sore from watching too many women demean themselves in movies.

Writers Niels Mueller and Heather McGowan, whose words were shot on digital video by savvy director Gary Winick, do not dwell on the social unacceptability of the various issues brought up in “Tadpole.” At the center is teen-age love, not romantic taboos, and this modest, trifling comedy does the matter justice.

A (1 hr., 18 min.; PG-13, some profanity and mild sexuality.)