Mischievous Lady Margaret School pupils gave head Sally Whyte a fright before eventually emerging with outstanding overall grades.
She said: "We were quite concerned at one point because they were quite a lively year. But after the mocks they really knuckled down and have done exceptionally."
Ninety per cent of the school's 90 pupils gained five or more A*-C grades including English and maths, while 24 girls got straight As and A*s.
Among the top performers was Emmy Taylor from Barons Court, who celebrated scoring eight As and two A*s by jetting to Venice with mother Pam.
"I'm so pleased," said Pam. "We can go abroad to celebrate rather than commiserate so we're really happy. She's worked so hard, she didn't waste any time and really knuckled down."
Emmy said: "I genuinely thought I was going to fail some of these so to get the results I did is beyond what I thought was possible."
Sophie Holmes , from Putney, did even better, recording six A*s in English, religious studies, history, biology, chemistry and Spanish.
"Doing so well in religious studies was a massive surprise because it's probably my least favourite subject," she said. "I'm really pleased because I had to work really hard."
Friend Rachel Hunter , from Kew Gardens, went from getting Cs and Ds in her mocks to an impressive four A*s and five As in th realy thing.
She said: "The mock results made me wake up and start to revise properly."
