Sam Dawson (Sean Penn) is a 40-year-old mentally retarded man who finds himself with a daughter after a one-night-stand. Working at Starbucks and getting help from a kindly neighbor (Dianne Wiest), Sam is able to successfully raise his child, Lucy (Dakota Fanning), on his own. With Lucy's seventh birthday approaching, a predicament arises: Sam has the brain capacity of a 7-year-old himself, and what will he do when Lucy surpasses his level of intelligence?

Through a misunderstanding that gets Sam arrested for allegedly attempting to solicit a prostitute, Lucy is taken away from him. Not knowing what to do, Sam is coaxed by his buddies to hire a lawyer to take the case to court so he can regain custody of his daughter. The attorney he chooses, and who agrees to take the case on pro bono simply to impress her colleagues, is Rita Harrison (Michelle Pfeiffer), a short-tempered, high-powered woman whose job keeps her away from her own young son.

The two major relationships followed is that of Sam and Lucy, and Sam and Rita. While Sam and Lucy have a beautifully loving bond, the question posed is whether love is enough when you are trying to raise a child more advanced than the parent. Meanwhile, the shallow Rita ends up learning more from Sam than he learns from her, namely how to grow a conscience and much-needed empathy.

Thoughtful and emotionally rewarding, "I Am Sam" works more successfully than it has any right to. The courtroom storyline is a by-now stock plot element that, if not treated with the right tone and style, often resembles a movie appearing on the Lifetime network. The distinct and honest treatment of the characters here overcomes this dubious risk, and their personal growth is invigorated with a sure, poignant hand that mostly avoids mawkishness.

Portraying a type of character he has never tried out before, Sean Penn (1998's "Hurlyburly") is exceptional and sympathetic as Sam, even when his handicap causes him to become difficult and stubborn. Playing a mentally retarded person on film is a tricky task. It may sound relatively easy, but the emotions and body movements have to seem genuine, rather than acted. Penn never once breaks from the role, and more than ably becomes the center of the picture.

Opposite Penn is Michelle Pfeiffer (2000's "What Lies Beneath") as attorney Rita Harrison. No fault of Pfeiffer's, as she was likely directed to act the way she does, but Rita is set up in the first half as an appalling individual without one redeeming quality about her. She is close-minded, snobbish, and greedy. It is only as the film progresses that she manages to understand and befriend Sam's position, and put what she has learned from him into action with her own neglected family. Pfeiffer holds her own against Penn, but is simply not very likable.

As 7-year-old Lucy, what can be said about newcomer Dakota Fanning other than that her performance is the best of someone as young as she since 4-year-old Victoire Thivisol's powerhouse turn in 1997's "Ponette." Fanning is not just an adorably cute child, but also surprisingly unaffected and touching. She has some of the most difficult scenes in the picture, and handles each one like a pro who has been doing this far longer than her age suggests.

Rounding out the top-notch cast are Laura Dern (2001's "Novocaine"), marvelous in the superbly written supporting role of Lucy's understanding new foster mother; the incomparable, underworked Dianne Wiest (1998's "Practical Magic") as Lucy's godmother; Loretta Devine (1998's "Urban Legend" and 2000's "Urban Legends: Final Cut") as social service worker Margaret Calgrove; and Doug Hutchison (1999's "The Green Mile"), effortlessly disappearing into the part of Sam's autistic friend who has an affinity for movies.

Occasional moments in "I Am Sam" are left to play out for so long that they lose their effectiveness, no more than Rita's emotional breakdown scene. The turning point for Rita as she pours out her soul to Sam, Pfeiffer does a plaudatory job, but subtle flaws in her work are wrongfully exposed by an editor who seemingly fell asleep while working on the scene. By going on for what seemed like an eternity, Pfeiffer's big moment passes over the point of poignancy to become emotionally sterile. Comparatively, a dramatic scene late in the film between Dern and Penn is flawlessly handled, and earns all of the deep emotions it sets out to achieve.

With a memorable soundtrack made up of Beatles cover tunes (Sam's favorite musicians) and hand-held cinematography by Elliot Davis (2000's "The Next Best Thing") that injects a stirring authenticity to the characters' dilemmas, "I Am Sam" is strong enough work from director Jessie Nelson to stand above the crowd of similar films. Through the course of its somewhat overlong 132 minutes, we grow to care about and love Sam, Lucy, and almost everyone else involved. And as The Beatles' and Sam's motto goes, "All you need is love."