Every so often I challenge myself to watch a film that I might not usually go to. An American High School coming-of-age movie would not be my first choice, but since Lady Bird seemed to be dividing opinion between critics and audience, I thought I’d review it before it either did or didn’t win an Oscar.

First off, I was wrong-footed by the title, as I thought of the nursery rhyme: “Ladybird, Ladybird, Fly away home.” It was a far-cry from Ken Loach’s harrowing Ladybird, Ladybird, and Carroll Ballard’s sweet film, Fly Away Home with Anna Paquin – who also plays in Kenneth Lonergan’s sadly misfired masterpiece, Margaret. I’ll return to this film presently. Lady Bird seems a more straight-forward film at first, following the eponymous (albeit, self-named) character on her ‘voyage of self-discovery.’ And, yes, that’s a cliché.

So are many of the tropes of teenage angst clichéd: parents, peer-groups, various graduation events both personal and academic. But the subtlety of this story lies in the focus. It’s not necessarily about the main character. Saoirse Ronan’s portrayal of this sassy, funny, slightly geeky but endearing teen who goes by the nickname Lady Bird is pretty flawless (apart from her skin, which is gloriously pocked with acne, and her forearm which is clumsily caste in pink plaster, for seemingly unexplained reasons.)

Her humour and perspicacity constantly backfire, due to her innocence. She seems closer to thirteen than eighteen (but not the kids portrayed in Thirteen) while at other times she has the wisdom – and wit – of Juno (as in, Juno.) But, above all, she has ambition. Her aim to survive the strictures of a Catholic Education (at the School Dance the couples are told to “leave six inches for the Holy Spirit”) and her escape from small-town Sacramento seems hampered not only by her background and dubious abilities, but also, by her parents.

As we move through the year, beginning with the School Musical Production (with snips of sardonic songs from Sondheim’s Merrily We Roll Along: ‘It started out with a Song’ and ‘Good Friends’) to Thanksgiving, Christmas, then headlong into Prom Season we see the usual fare of this kind of movie. Lady Bird falls in love (well, sort of) with the wrong people, mixes with the wrong sorts, loses her best friend and her virginity in a fairly unspectacular way (but not without humour and hubris) and – most important – puts a huge rift between herself and her mother as she pursues her selfish dream of flying away to study in New York.

For some, with this type of film, Cruel Intentions is the benchmark for bitchiness; Carrie for creepy nastiness, and – my personal choice – Margaret is the perfect post-9-11 analogy for America’s coming of age (it’s a shame Lonergan shot that film in the foot by insisting on his far-too-long cut… but, that’s another story.) Greta Gerwig, directing for the first time, has screenwriting credentials, yet her attempt to hint at politics doesn’t quite hit the spot, although the choice of year may be significant.

But most people watching this film will be there for the humour and feel-good. That stuff is in abundance, despite the ‘ouch’ moments between mother and daughter, and the highly nuanced, if painful, family dynamics. When Lady Bird’s plaster caste is removed, it cracks apart like the wings of our fragile character splitting open. What does the nursery rhyme ‘Ladybird fly away home’ really mean? Like the plot of Merrily We Roll Along, the idea seems to work chronologically backward: fly away home…?

It seems that, despite their warring personalities, mother and daughter will never come to realise the meaning of ‘home’ until the latter spreads her wings and flies away. At this point, we realise that this film is more about the mother – expertly played here by Laurie Metcalf – wanting the best for her child while, at the same time, unable to let go and allow her daughter to be her best self. It’s hard to say if the ending was conclusive in this respect. Perhaps this Lady Bird will continue to fly, and at some point we’ll see the next passage of her ‘voyage of discovery.’

(I don’t want to end with this cliché. Suffice it to say, it didn’t win an Oscar… but go and see it anyway!)

Lady Bird is screening at the Filmhouse, Edinburgh until 22nd March.