Brimming with spirit and snappy dialogue, Lady Bird is the feature-film debut of actor, screenwriter and now director Greta Gerwig. Loosely based on Gerwig’s own experience growing up in Sacramento, the story follows the senior year of Christine “Lady Bird” McPherson (Saoirse Ronan) and her drive to shed the constraints of family and Catholic high school as she launches herself into adult life.

High school coming-of-age tales have been explored from every angle, yet Gerwig and Ronan manage to infuse this particular version with freshness from the outset.

The film opens with Lady Bird throwing herself from a moving car to escape her mother’s hypercritical conversation and she sports a hot-pink cast through much of the film as a result. Lady Bird’s relationship with her parents, particularly her mother Marion (Laurie Metcalf), is central to the film, and Metcalf is brilliant, clearly relishing the complexity of the role.

Despite travelling well-worn territory, Lady Bird proves to be a vivid and original protagonist, primarily in that she is not particularly exceptional. Mildly rebellious, all she really wants is to escape Sacramento and start a new life. The name “Lady Bird” is part of that plan, a means of asserting a new identity and infuriating her parents in the process.

The film is set in 2002, with the financial crash still over the horizon, yet the McPhersons are already struggling financially. Lady Bird’s quiet and depressed father Larry (Tracy Letts) has been retrenched and can’t find work. Marion is a psych nurse and continually needs to pick up extra shifts to make ends meet, explaining her perennial bad mood and lack of patience for Lady Bird’s budding pretentiousness.

The film’s originality is not in the story so much as the dialogue and the keenly observed details of middle-class suburban life.

The structure and content of the film mostly adhere to the well-worn traditions of high-school comedies. There are the relationship dramas, initially with the unthreatening theatre geek, Danny (Lucas Hedges), then the pretentious poser, Kyle (Timothée Chalamet). The best-friend dilemma also raises its head; long-time bestie Julie (Beanie Feldstein) is dumped to secure the attentions of the self-obsessed queen bee (Odeya Rush).

Despite the familiarity of rhythm and plot, there is still much to appreciate. The tensions of family life, particularly the fraught mother-daughter relationship, have a discernable sub-current of warmth and love that stops them slipping into caricature.

Ronan’s portrayal of a youthful Gerwig is uncanny, her capture of gesture and cadence so nuanced as to make this reviewer forget for long stretches that I was not watching Gerwig herself.

This film is a surprisingly mature work from a new director who is clearly focused on creating stories brimming with clever, naturalistic dialogue and keen observations of people, class and place. This subtle and perceptive coming-of-age film announces Gerwig as a fully-fledged director whose career, I suspect, will be well worth following.