THE core of this gentle drama is not the mathematical genius of its seven-year-old central character, Mary (Mckenna Grace), but who has the right to custody of her.

Shortly after Mary’s mother bore Mary by a father whose name nobody in her family knew, her mother gave the baby into the care of her brother Frank (Chris Evans) then suicided.

We first meet Mary and Frank living in a rented cabin in Florida. In a violent outburst, Mary who’s just started school there tells class teacher Miss Stevenson (Jenny Slate) that it’s not challenging her intelligence. This is a level of performance skill that might make a sensitive viewer wonder where the film is going from that point. Mary reinforces that concern when she breaks a model zoo over the head of a bullying boy.

But have no fear on that account. Mckenna Grace is a child prodigy in the acting department. As the film develops, Mary confronts not only the school authorities but also her formidable maternal grandmother Evelyn (British actress Lindsay Duncan, in her late sixties not holding back from close-ups filming wrinkles and all of a face that was never less than beautiful).

Evelyn took a degree in mathematics from Cambridge. Tom Flynn’s screenplay proposes that Mary’s mother not only inherited that window into genius but also passed it on to Mary. Accept that possibility or reject it, as you choose. For the film’s purposes, it’s a given element of the drama that works well enough.

By the time the dust has settled around Evelyn’s determination to take possession of Mary and send her to a special school for gifted kids despite Frank’s determination that Mary will grow up in normal social and intellectual environments, the film has evolved into a warm account of a child’s needs for access to both those growing up paths.

The whole cast is first-class. The screenplay comes to terms with complex issues. And Mary fills a blackboard with mathematical symbols leading to an undeniable QED. If you don’t know what that means, your education may well not have included pure mathematics, which is regrettable.

At Palace Electric, Dendy, Capitol 6 and Hoyts Woden