Seventeen-year-old Alex McDonald sat hunched in his chair, his long dark hair obscuring his face, staring resolutely at the paper in front of him, but this was no sulk. From the large pad on his knee, a pair of charcoal-rimmed eyes seemed to burn from the paper – his own eyes, in a freely rendered self-portrait.

On Saturday Alex, along with 25 other young people between 11 to 18, travelled to Tate Modern to take part in a drawing masterclass given by the Professor of Drawing at Chelsea College, Stephen Farthing, and the artist Ray Wilkinson. As winners of the Tate Times Drawing Challenge, they also came to see their original competition entries, simple self-portraits on A4 paper, in pencil, crayon or charcoal, framed and displayed in a special exhibition at Tate Modern itself.

“I don’t know why we’re here,” admitted Wilkinson, “You’re all already artists.” He talked about the wildly differing styles that had been chosen for the exhibition. “There’s no right or wrong way to draw.”

“Our objective,” added Professor Farthing, “is to help you make a better drawing than you’ve ever done before.”

While some politely shared out paper and drawing equipment, Wilkinson took out eight of the students to look again at the exhibition and to discuss the work. The first picture they came to was that of 16-year-old Marina Gardiner, who had drawn herself as Elizabeth I. Marina laughingly explained that she enjoyed drawing intricate patterns, like those on the dress in the picture, and didn’t really see herself as a queen, and as she did so it became clear that, far from disguising her personality, the portrait expressed her ebullient sense of fun.

As the group went down the line of pictures, people came forward to offer thoughts, to claim their own portraits – some shyly, some eagerly.

Back in the class, the silence of fierce concentration reigned, except where Professor Farthing was offering help. Sitting down with Rosie Lom, 11, he showed her how to embark on a nose, by drawing the greyness and shade around it.

Too soon for many, the class was over and the drawings put up on the windows. Many were breathtakingly good. Professor Farthing was pleased. “It’s interesting how much better they’ve done. They’ve ploughed their own resources deeper. Most of them are perfectly capable of making an image that looks like themselves. The most difficult thing is capturing personality.”

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