Rapid ageing usually forms part of a horror film.

Here it provides a showcase for Robin Williams as a 10-year-old boy embarrassingly trapped inside a 40-year-old body.

We, too, are embarrassed at the situations into which the adult-looking Williams is forced at school but he, like the film, comes good in a triumphant finale when, as a 17-year-old graduate looking 68, he tells parents and fellow-students that his life has been brilliant and spectacular.

Love him or loathe him, Williams is virtually the whole show, although Diane Lane is unexpectedly good as his spirited mother.