James L. Brooks is a well-respected man, having written and directed “Terms of Endearment,” “Broadcast News,” “I’ll Do Anything” and “As Good As It Gets,” not to mention being one of the creators of such beloved TV shows as “The Mary Tyler Moore Show,” “Taxi” and “The Simpsons.” So it’s unfortunate to see him make mistakes the way he does in “Spanglish.”

This is an uneasy, tiring film, full of great material here, weighed down by mediocrity there. At the 90-minute mark, I thought, “Well, this is wrapping up nicely. A solid B-grade film if ever I saw one!” By the time the film actually ended, 40 minutes later, my sentiments were not nearly as charitable, and my assessment had dropped down to a C+. And there were STILL plot threads left unresolved.

The movie is narrated by young Cristina Moreno (Shelbie Bruce), a Mexican girl who traveled to Los Angeles with her beautiful mother Flor (Paz Vega) to find a better life for themselves. But only now, six years later, do they actually venture outside the Latino barrios of L.A. and into white America, when Flor is hired as a housekeeper and nanny for the Clasky family.

The Claskys are Deborah (Tea Leoni), a neurotic, self-absorbed woman who has recently been downsized from the professional world into the world of housewifery; and her husband John (Adam Sandler), a modest, easy-going chef who is just now becoming a celebrity for it. They have two children, Bernice (Sarah Steele) and Georgie (Ian Hyland), though I think the latter gets only about 90 seconds of screen time, and both youngsters disappear for a good half-hour of the movie. Deborah’s mother Evelyn (Cloris Leachman), once a jazz recording star and now a full-time chipper alcoholic, lives with them in their sunny, spacious Los Angeles home.

Flor speaks barely a word of English but is able to take charge of the Clasky household nonetheless, retaining her own privacy — the Claskys don’t even know she has a daughter at first — while she works. When Deborah criticizes Bernice for being slightly overweight, Flor comes to the rescue in a very sweet and endearing moment. Young Sarah Steele, making her first film appearance, is wonderfully real as the awkward tween Bernice, so full of life and personality. Paz Vega is beguiling as Flor, too, and so we have the makings of a good film here.

Alas, we are forced to spend time with John and Deborah Clasky, too. Deborah is an unlikable shrew masquerading as a “flawed character” with “issues.” She’s a hateful b-word, pure and simple, so caught up in her own self-doubt that she forgets anyone else exists. I kept wanting her to have an affair so that John would have an excuse to divorce her, except that John, inexplicably, is in love with her.

John is a far more likable character, but he is played by entirely the wrong actor. We are asked to accept Adam Sandler as a father and a world-famous chef. He is almost convincing in the former role; as the latter, he is not even close. Evidently his much-ballyhooed dramatic work in “Punch-Drunk Love” was a fluke, because his attempts at depth here are just embarrassing, like a stoner plucked out of a frat house to act opposite Sir John Gielgud in “Hamlet.”

The plot ambles around a lot of areas, including John’s growing affection for Flor, Flor’s fierce protection of Cristina, Cristina’s desire to be less sheltered, and Deborah’s world-class jackassedness. Through it all there are incidents or scenes that are funny or effective. Most of what Cloris Leachman does as Evelyn is amusing, leading up to the moment she tells her daughter Deborah that “lately your low self-esteem is just good common sense.” And there is one especially noteworthy scene between John, Cristina and Flor, an argument over how all the children are being raised, with Cristina providing translation and cutely enacting her mother’s fiery sentiments.

But Brooks seems to think that giving characters self-doubt is the same as giving them an arc, when in fact that is only true if they somehow address, resolve or deal with their self-doubt. John, for example, doesn’t want to be the world’s top chef because he fears the pressure it will bring. He achieves the distinction anyway, though, and is soon crushed by the responsibilities of it, just as he feared. But does he learn how to cope with it, or root out the source of his self-doubt? Nope. He just doubts for a long time, and then the movie ends.

Too, the marriage of John and Deborah is a difficult one, a matter that is given a good deal of screen time. Yet in the final analysis we are left to guess what’s going to happen to them, because the film has switched back to its original protagonist, Flor.

Don’t waste my time, movie. Either tell someone’s story or don’t. Introducing characters and spending inordinate amounts of time dealing with them, only to abandon them in the end, is not acceptable.

And so the film is tragically uneven, filled with laughter sometimes and marred by impatient watch-checking other times. It needs to be trimmed, toned and focused better before it is put on public display — but since it’s too late for that, it probably just needs to be disregarded.

C (2 hrs., 10 min.; PG-13, one F-word, some other profanity, a little sexuality.)