Twenty pairs of eyes shone with effort as the children's fingers danced on the beads of their abacus in tune to their tutor's incantation of numbers.
The figures rattled out by the second, each greeted with a telltale clacking, for 10 minutes until the counting machines were laid aside. The pupils closed their eyes and began in unison to pluck at the air as if at ghostly violin strings.
It is a scene with the feel of a century-old learning regimen, pre-calculator, pre-creativity. But this is Wan Chai in 2001: welcome to the William Wu Training Centre. After three years of study, children at the centre can now give a near-instant answer to the addition of 150 double-digit numbers read aloud. Nor do they have higher than average IQs, they are just normal eight- to 12-year-olds.
The abacus 'trick' echoes what many maths experts emphasise: the importance of allowing pupils to understand the meaning of numbers before they move on to calculation. 'Very often, students look at the digits only as symbols. But the beads on the abacus can help them visualise the meaning of numbers and improve their conceptual thinking. It will also help them to calculate faster,' said William Wu Fat, the training centre's founder, who has been studying the role of the abacus in maths for nearly 13 years.
Students normally take at least three months to familiarise themselves with the tool. After that, they graduate to calculating by moving their fingers only, as if there was an invisible abacus in front of them. The final stage is learning to calculate without movement, with an abacus in their minds only.
At the start, meanwhile, just using both hands to work on the abacus could stimulate the development of both sides of a child's brain, said Mr Wu. 'While the left brain is responsible for calculations, the right brain is projected with the image of the abacus,' he said. 'It is a misconception that good scientists only need a well developed left brain. The truth is that they will never have any original ideas if they do not possess an equally well developed right brain to give them the creativity.'