For those not familiar with it, 'I Am Sam' is about a retarded man trying to regain custody of his seven-year-old daughter.

There are two primary things that make this movie work. One is Sean Penn as Sam Dawson, the father whose mental age is the same as his daughter's. The other is Dakota Fanning as Sam's daughter, Lucy Diamond Dawson (the name is from the Beatles song, 'Lucy in the Sky with Diamonds').

Ultimately, of course, a movie like this depends first on its lead character, and the performance of the actor playing him (think Cliff Robertson as 'Charly,' for example, or Dustin Hoffman as 'Rain Man'). Sean Penn's portrayal of the mentally challenged dad is first rate. He succeeds in making Sam both believable and sympathetic.

However, even Penn's fine performance is not enough by itself. While Sam is the primary subject of the movie, the focus of the story is his daughter, Lucy. For the audience to truly be in Sam's corner in his custody fight, they needed to feel some of the same emotions toward her that Sam was feeling. They needed to fall in love with this little girl, so the thought of being her parent and having her taken away would cause deep emotional pain, forcing a strong identification with Sam's struggle to get her back. Thus, the casting of Lucy was just as important to the artistic success of the film as the casting of Sam.

To her everlasting credit, director Jessie Nelson fully understood the importance of this casting decision, and auditioned many little girls for the role until she finally found the right one - and there was only one 'right one' for this role in the whole world: Dakota Fanning. Lucy Dawson had to be believable, she had to be both precocious and have an air of innocence, and she had to be quintessentially lovable. Delivering the complexities of this role in the amounts needed to make 'I Am Sam' completely fulfill it's potential would have been impossible for any kid that would have been available even up to a year earlier.

It's been said that sometimes it's better to be lucky than good. In directing 'I Am Sam,' Jessie Nelson was both. She had the right vision, and by pure chance she timed the making of the film so that the only young actor who could have ever done justice to the role of Lucy Diamond Dawson was at precisely the right age to play her. Dakota Fanning delivered the greatest supporting little kid performance in the history of acting. Added to Sean Penn's portrayal of Sam, Dakota made the difference between 'I Am Sam' being just good, and being the truly great piece of cinematic art that it is.

'I Am Sam' is rated PG-13, primarily for strong language, which is almost exclusively used by the Rita Harrison character (Sam's lawyer), played by Michelle Pfeiffer. Michelle did a good job, as did most of the other cast members, especially Sam's group of friends. The only actor I didn't like was Richard Schiff as the prosecutor, whose performance would work well only as a sedative.

If you haven't seen this movie, I strongly recommend you buy the DVD as soon as possible. If you don't have a DVD player, buy one of those too. I did, and it was worth every penny. I further recommend that when you do get the movie, you set aside enough time to run it twice in a row. The first time, just let yourself experience the movie. Don't think about Sean or Dakota or acting at all, just let the whole thing flow in, and your emotions flow out. Then watch it a second time, while the emotions are still fresh in your mind, and observe Dakota's performance carefully. Notice all the subtle little nuances she used to maximize the emotional reactions of the audience. As you do this, ask yourself how someone so young could possibly have known how to do all that stuff so perfectly. Personally, I believe that no other little kid has ever been able to do what Dakota Fanning did in 'I Am Sam.' As far as I'm concerned she's an absolutely unique talent, the likes of which will probably never come along again. I, for one, am thankful to be sharing this world with her, and look forward to many more great performances from her for a long time to come.