SEX and religion, as Professor MacCulloch is currently reminding us on BBC2, are intimately related. The Falling (Cert. 15) clearly connects them. It opens with a tree, beautifully shot by Claire Denis's long-time cinematographer Agnès Godard - the scene, it emerges, of many a trysting. This eventually gives way to the repressed figure of Eileen (Maxine Peake), unable to look the world, and particularly at her daughter Lydia (Maisie Williams, best known as Arya Stark in HBO's Game of Thrones), in the eye.

The contrast is between life in decay (it is autumn) and adolescent contemplation of what the springtime of life will offer. A voiceover recites Wordsworth's "Intimations of Immortality", recalling a time when everything "did seem apparelled in celestial light", but these things "I can see no more".

While we never lose sight of home life, the emphasis shifts to school, full of hormonal girls forever talking about "it". Lydia's best friend Abbie (newcomer Florence Pugh) has recently had sex, more out of curiosity than desire. The two girls' own relationship verges on eroticism. This is the film title's first layer of meaning. Falling isn't a reference to schoolgirl crushes. It's 1969, when old restraints are jettisoned, boundaries are pushed in terms of conduct, and female sexuality is being explored.

When the pregnant Abbie collapses and dies, pupils under Lydia's leadership begin a second kind of falling: mimetic bouts of spontaneous fainting, usually during "non-denominational worship". A New Testament reading is interrupted by swooning teenagers, and the entranced Lydia is carried out, as if crucified, on her disciples' shoulders.

There's considerable evidence of mass psychogenic outbreaks both then and now. The film attributes this particular one to a generation of teachers, such as the stern Miss Mantel (Greta Scacchi), whose characters have been shaped by male oppression. One cannot quarrel with the director Carol Morley's good intentions, but the film would have been better served if only she had left more questions hanging. The film has been likened to Picnic at Hanging Rock (1975),inasmuch as it concerns strange occurrences around a group of schoolgirls, but Peter Weir (a director whom one Jesuit film colleague describes as a mystic) fills the screen with haunting but inconclusive images.

The Falling tries to explain it all away, not least in terms of what religion does to sex. The result is not exactly The Devils  meets The Crucible, but it is suggested that the girls' out-of-body transcendent experiences are an alternative outlet in the face of sexual subjugation imposed by Christian norms. Wordsworth is trotted out again at this point. Women such as Eileen and the teachers, shaped by a former age, may have forgotten the joy of being alive, whereas Lydia and others still believe that "trailing clouds of glory do we come From God."

It is all admirable, but the film makes far too simplistic an equation between sexual awakening and what it means to turn into fully realised women. Implicitly, organised religion is blamed for hindering this process. To be frank, The Falling is too earnest for its own good, turning alarm into risibility. The audience will have got the point long before the eighth or ninth fainting fit occurs. The same goes for repetitive images of the old oak. One ceases, out of boredom, to ponder what important questions it or indeed the film as a whole are posing - which is a pity.

On release from today.