A natural heir to high-school mavericks like Ferris Bueller and Rushmore’s Max Fischer, Charlie Bartlett is neither as smug as the former nor as creepy as the latter.

Blessed with the puppyish charm of Anton Yelchin (of underrated drama Alpha Dog and soon to appear in both JJ Abrams’ re-energised Star Trek and Terminator 4), he is what Doogie Howser might have become had he studied business rather than medicine.

Yet despite the best palm-greasing efforts of his mother (Davis, in the regulation kooky rich parent role), the young entrepreneur is expelled from yet another private school for selling fake driving licences.

Sent to the local high, his friendly manner and preppy togs make him a prime target for school bully Murphy (Tyler Hilton).

The pummelling prompts his mother to call for the psychiatrist, but Charlie senses that it’s the rest of the school who need help – starting with Murphy.

Unlikely as it seems, the pair become business partners. With Murphy minding the stall and Charlie’s shrink unwittingly supplying the prescription meds, the psychiatric service soon has troubled teens queuing round the toilet block.

But though booze-battling Principal Gardner (Downey) is probably more disaffected than any of his students, he refuses to have his authority further undermined by some preppy troublemaker who’s got the whole school on a Ritalin rush.

Yet as Freudian luck would have it, Gardner’s daughter Susan (cuddly Kat Dennings) has fallen for Charlie. It’s hard to say who that puts in the worst position.

In his directorial debut, Austin Powers/Meet the Parents editor Jon Poll finds it difficult to strike a satisfying balance between tone and content.

The light (and somewhat routine) quirkiness of the opening scenes lays a weak foundation for the heavier issues to follow.

From freedom of speech and the right to privacy to depression, aggression and suicide, the film holds some facile views.

Nobody will miss the irony of Robert Downey Jr delivering lectures on drug misuse and personal responsibility, but he as much as anyone will know that it takes more to banish the blues than a snog and a sing-song.

The unevenness extends to character. Charlie – like his mother - is only a misfit when it suits, with his rise to popularity being as unlikely as Murphy’s transformation from boot-boy to amateur thespian.

Thankfully, a generous sprinkling of wit (“We should go wine-tasting – we haven’t done that since you were six!”) and engaging performances from Yeltsin and Dennings keep Bartlett from going pear-shaped.

Elliott Noble