"He ain't stupid, he's retarded," says Lior Liebling's father Mordecai. "It's different." His is one of the refreshingly blunt utterances that keep Praying With Lior, Ilana Trachtman's documentary about a boy with Down syndrome about to have his Bar Mitzvah, from dissolving into gunky disingenuousness.

Last fall an outcry came from Down parents when it was announced that all pregnant women -- not just those over 35 -- would be screened for the syndrome, giving them the option to terminate. The parents argued that having a Down syndrome child was "a blessing", a "great opportunity" that should be cherished and not avoided at all costs. Frankly, that argument against screening disgusted me, so when family members of Lior, early in Trachtman's film, began describing the affable 12-year-old as "closer to God" than the rest of us, due to having "fewer veils," I got my cynical guard up.

What Lior has is an extra chromosome -- 47 instead of the 46 that his two sisters and brother were born with. Their mother, Rabbi Devorah Bartnoff, instilled in all of her children her deeply seated Jewish faith before her death from breast cancer in 1997, but it was Lior, her second-youngest, who engaged in prayer with a fervor that spurred and rivaled hers. Trachtman intercuts home movie footage of the Liebling family and Lior as a toddler, sing-songing and chanting along with his mother to Hebrew prayers ("davening" is the Yiddish term) with her own footage of the family preparing for what everyone agrees will be the biggest event of Lior's life, his Bar Mitzvah. The home movie vibe carries over, however, especially in Trachtman's interviews with Lior, in which brightly voiced questions are peppered at a clearly antsy child, and in the extended sequences lingering over events most of us will go to great lengths to avoid: a little league game, a 7th grade classroom full of boys, a dinner table full of bickering children and, well, a Bar Mitzvah.

Lior is sweet, needy, bossy and clearly the baby of the family, a fact the actual baby of the family, his little sister Anna, points out with barely contained contempt. Lior is certainly high functioning, a fact pointed out almost cruelly by Trachtman's repeated juxtaposition of him with more severely retarded children. He answers many of the director's leading questions with Zen koans ("What does God look like?" "God is God.") that she seems to include hoping they err on the side of profundity. She also includes, however, footage of a family friend rebutting the theory that the hard-praying child is a "spiritual genius," arguing that Lior's early attempts at prayer were vigorously validated, and that had the same thing happened with, say, Christmas carols, he would be singing "O Tannenbaum" at the top of his lungs today. It's an argument that applies to all religious upbringings, but is particularly apt given Lior's disability and its manifestation in his love of repetition and eagerness to please. Lior's father also eventually expresses his reservations over the grandiose ideas people project onto his son, whom he drives toward goals that may be beyond his reach.

The most interesting aspect of Lior's story is that of the family members who love and care for him. Mordecai remarried after Devora's death, and there are several intriguing, if brief, looks at the complex family dynamic at play in not just Lior's care but that of his three siblings. Lior's relationship with his brother Yoni is particularly poignant, and the scene in which the extremely loving and loyal Yoni muses over how his entire life will essentially be circumscribed by his brother is both heartwarming and heartbreaking. Littlest sister Anna is also a pocket powder keg waiting to blow, but Trachtman leaves her be as well. Eldest child Reena admits to having been a mother figure for her siblings, especially Lior, another loaded statement that goes unexplored; all we get is her look of smoldering resentment when Lior's stepmom drops the ball during a discussion of honoring Devora's memory at the Bar Mitzvah.

Everyone loves an underdog, of course, and from Murderball to Billy the Kid to possibly the greatest thing I have ever seen, this clip of an autistic teen winning the big game for his school, disabled underdogs attract documentary filmmakers as often as health care and genocide. When Lior finally brings the room to its knees, nailing the Torah reading at his Bar Mitzvah, it is a highly emotional, affecting moment -- truly an underdog weeper for the ages. I only wish the 80 minutes that preceded it had been as powerful.