It's tempting to think that dramatising The Prime of Miss Jean Brodie is as easy as passing an exam simply by signing your name on top of the paper. It is almost as though Muriel Spark had one eye on Broadway when she sat down to write what is still held up, some 20 novels later, as her tour de force. Miss Brodie's flamboyant predilection for "Art, Truth and Beauty", the spiritual doctrine with which she galvanises her coterie of pupils at the Marcia Blane School, conveniently goes hand-in- hand with a boundless capacity for memorable one-liners. "Give me a girl at an impressionable age, and she is mine for life," runs her refrain. She might as well be saying to her creator: "Give me an audience at an impressionable time of the evening and they'll be quoting me for life."

Jay Presson Allen was in there like a shot soon after the novel was published in 1961, firing off stage and screen versions, both of which made chronological sense of the temporally disordered narrative. In 1966, Vanessa Redgrave took to the stage as the regal/renegade character-builder at Wyndham's Theatre. Two years later, Maggie Smith ensured that a snooty Morningside accent would permanently hover over the phrase "creme de la creme".

All teachers are, to some extent, actors - and what they impart to their pupils is as much the intangible art of self-presentation, and self-invention as any particular body of knowledge. In the case of The Prime of Miss Jean Brodie, this sense of theatricality is heightened by the exaggerated role-play between Brodie and her surrogate brood. Eunice Gardiner, famous for her somersaults, describes her mentor as "an Edinburgh Festival all on her own". Brodie commands her girls to walk "like Sybil Thorndike, a woman of noble mien". She pooh-poohs the idea of team spirit - "Where would the team spirit have got Sybil Thorndike?" She gives her followers lines to say to her enemy, the headteacher Miss Mackay. Brodie never allows herself to be upstaged. Even the infatuation with the Italian fascisti that proves her professional downfall can be partially excused by a whimsical attachment to the costumes of Mussolini's marchers.

The danger, of course, is that it all transfers too easily to the stage: the actress bathing in the soppy approval of an audience hankering after bygone eccentricity just as Brodie basks in the applause of those too young to know any better. Or worse still, that the star plays up the subtext of spinsterly sexual frustration ("That is not what I call education, I call it intrusion, from the Latin root prefix in meaning `in' and the stem, trudo, I thrust").

The nightmare scenario is Robin Williams's performance in Dead Poets Society - that mawkish travesty of the energising pedagogue. Brodie is trapped behind her repartee, her mantra about being in her prime sounding a desperate note that only others can hear. It takes a performance of enormous subtlety to suggest the vicarious, emotional half-life behind the wit, and also the genuine radicalism.

It's heartening that the director, Phyllida Lloyd, went back to the novel rather than the stage-play to ground the revival that opens at the National Theatre this week. It's reassuring to note that she is passionately persuaded that the book's governing image is not quaint but controversial ("It's all about the national curriculum versus the unpackageable alternative, the question of whether you plan education in advance or allow for imaginative responses to individual children," she said recently).

Above all, you know this won't be Brodie by rote because she's got Fiona Shaw (above) on board: erudite, mercurial, possessed of a temperament that can immersion-heat from steely to warm in seconds.

That's right, "creme de la creme".

`The Prime of Miss Jean Brodie', now previewing, opens 25 Jun, Lyttelton, Royal National Theatre, SE1 (0171-452 3000) 7.30pm