I first noticed actress Saoirse Ronan two years ago when she starred in “Brooklyn.” She had done other movies, but that was her breakout role. Now she’s really getting noticed for her work in “Lady Bird,” and every bit of praise is well-deserved.

When the title was included this summer in a list of upcoming films, I thought it was going to be about Lady Bird Johnson, onetime First Lady of the United States. After all, its release more or less coincided with that of Rob Reiner’s “LBJ,” with Woody Harrelson in ridiculous makeup as the 36th president. But this “Lady Bird” has nothing to do with that one.

Ronan is fantastic as Christine McPherson, a 17-year-old who, for reasons unexplained, wants everyone to call her Lady Bird. Chalk it up to teenage rebellion, and there’s lots of that in this character as she navigates her way through a Catholic high school, dating, a school play, applying to college, and the everyday frustrations of pretty much every human who’s ever been that age. It’s a time in life for expressing your individuality, and Lady Bird doesn’t miss an opportunity to do so.

That means a lot of clashes with her mother, Marion (Laurie Metcalf), who loves her daughter but doesn’t much like her. Marion — already stressed from having to work double shifts as a hospital nurse because her husband (Tracy Letts) is having problems at his job — is constantly disappointed in Lady Bird. She’s weary of their battles over every little thing, not the least of which is her daughter refusing to use the name she was given at birth. Marion has impossibly high standards and a near-aversion to happiness, which doesn’t make for the smoothest home life.

That relationship, at the core of the movie, is about all of the other issues that will be recognized by anyone who’s been exposed to the dynamic between a mother and her 17-year-old daughter, best summed up in this exchange in a clothing store where they can’t agree on a prom dress:

Marion: I just want you to be the very best version of yourself.

Lady Bird: But what if this is the best version?

The other characters in Lady Bird’s life — her best friend, her new best friend, the boys she’s interested in, her brother and his girlfriend, the teachers — seem familiar, but don’t spew the usual cliched dialogue you expect in a movie like this.

That’s what makes “Lady Bird” work so well. Greta Gerwig — a critical favorite for her work in Noah Baumbach movies like “Frances Ha” and “Mistress America” — hits just the right tone in her directorial debut. Gerwig’s script is based in part on her own youth, growing up in Sacramento. She knows these characters and how they’d sound in real life, which keeps them from being boring or predictable.

Like its title character, “Lady Bird” isn’t perfect, but it’s the best view of this world we’ve seen in a long time. It also contains two must-see performances by Ronan (the Irish newcomer who portrays a northern Californian without a trace of an accent) and Metcalf (a veteran star of TV and Broadway whose silent driving scene towards the end of the movie is the best acting you’ll see this year). They, and the movie, will surely get more well-deserved attention when Oscar nominations are announced.

I give “Lady Bird” an 8.5 out of 10.