DAVID HOCKNEY first went to art school because his precocious talent for drawing was spotted by teachers who had the liberal notion that it was no bad thing for a lad to become an artist. That was a long time ago, in 1953, but there is still a feeling of precocity in Hockney's work. There are many hints of laddishness too, and a pleasure in being taken up by senior figures, whether they be Thirties poets, museum directors or moguls of the international opera circuit. The Royal Academy's retrospective of Hockney's drawing demonstrates that work on paper suits his personality His paintings are, by comparison, laborious. But where, one asks, are the drawings of Hockney's maturity? Why is the show so bright at first and latterly so sad, with no substantial achievement at its centre? Mainly, I think, because of his departure from Britain as soon as his fashionable success was assured. He went to Los Angeles in 1964, just after he left the Royal College of Art The decision was the crucial moment in Hockney's career We are often told his reasons. Britain was grey, bureaucratic, and discriminated against homosexuals In southern California there were boys, fun and sunshine.

These were good reasons to leave (though not everybody thinks that Sixties London bore down too heavily on a free life) However, much was lost. Los Angeles has its place in the public imagination, but it is no art centre. And that's exactly what Hockney needed: the company of a serious, critical and inspiring avant-garde. Whatever his fame, he has always been on the margins of modern art. Hence the importance of his earliest period as a student, when he really was surrounded by clever and creative people. The RA show begins with some exercises - in the form of conventional life drawings and an elaborate set-piece of a skeleton - then becomes much more vivid and personal, as Hockney looked around for his own kind of art.

Obviously he wanted some sort of lightness, and it's interesting to see how he punctured the ponderousness of current British art. His very nice drawing of a Ty-Phoo tea packet, for instance, is almost a parody of the domestic grit favoured by painters of the kitchen-sink school. Then there are some cheerful sheets derived from public-lavatory graffiti. Hockney evidently liked putting words and signs in his drawings.

This makes them even more puckish, as though a boy had done them in an exercise book. He may have learnt the trick from the US painter Larry Rivers, or perhaps Dubuffet. In any case, it suited Hockney very well and, on occasion, still does.In the stimulating atmosphere of the RCA (and of London rather than his native Bradford) Hockney began to make his own style It's rather elusive, though instantly recognisable. He has always - and vehemently - denied that he had anything to do with Pop Art, and I think this is true.