It was the sound of cheers and delighted screaming from nearby Stratford that alerted pupils and staff at Eastleigh community school that London had done it.
Within minutes all 1,200 pupils at the school were celebrating.
Eastleigh is the secondary nearest to the proposed Olympic site for the 2012 games. Ann Palmer, the head, said: "The pupils are ecstatic and understand fully the immense significance of what is going to happen here."
At Carpenters primary, also near the Olympic site, pupils burst into a spontaneous conga on hearing the announcement. Freddy Johnson, aged 10, said: "This is one of the best things that will happen in my lifetime.
I can't wait to meet people from different countries."
Langdon school, Newham, east London, sent 26 pupils to Singapore to help sway the voting. Vanessa Wiseman, the head, said: "Young people across five boroughs have been part of this bid, showing the diversity of London. They have all been so proud and wanted to show that London is a great city."
Atif Zafar, 16, a pupil at Langdon, was in Singapore on Wednesday when the decision was taken: "When we heard it was London everyone went up in the air. There were no feet on the ground."
Ashley Mitchell, 15, a national swimming champion, was also in Singapore with other pupils from Forest school in east London: "If I keep my training up I should be able to take part in the Olympics in London," he said.
Schools elsewhere in London proudly celebrated the news.
Michelle Moore, community development manager at Eltham Green school, said:
"Everybody was jumping. The eyes of the whole world will be on London."