Shanghai's 15-year-olds are still the best in the world at reading, maths and science, according to the latest global survey.
Hong Kong's youngsters ranked second in science and reading - up from third and fourth in 2009 - and held their third place for maths.
But compared with their counterparts in Singapore - second in maths, and third in science and reading - Hong Kong pupils improved less, gaining only 11 points more in reading and six in maths and in science from the 2009 assessment. The Singaporeans gained 16 points in reading, 11 in maths and nine in science. Shanghai students also showed more improvement, gaining 14 points in reading and 13 in maths compared with 2009.
The assessments also showed that just 12 per cent of pupils in Hong Kong were top achievers in maths, well below the 30.8 per cent for Shanghai and 19 per cent in Singapore.
The latest report by the Programme for International Student Assessment (Pisa) was based on surveys of more than half a million 15-year-olds in 65 countries and regions.
Professor Esther Ho Sui-chu, director of the Centre for International Student Assessment in Hong Kong, said: "I think the differences in improvement are not very important."
She attributed those differences to the way cities treated the assessment.
"I don't know how Shanghai and Singapore did the assessment, but Hong Kong students did not prepare for the assessment and took it in a relaxed way," she said.
In April and May last year, 5,000 Hong Kong pupils from 148 government, aided and independent schools were randomly selected to take the assessments.
"We need to work on how to nurture more bright students, as our exam-orientated system tends to focus on high achievers' performance in exams but does not help them learn more than that," Ho said.
The difference in performance among pupils from the same school also increased, suggesting that the abilities of children within the same school vary more. And there were significant differences between the sexes in maths and reading, with boys outperforming girls by 15 points in maths and girls outscoring boys by 25 points in reading.
Ho said the government had to provide teachers with more resources to develop different teaching methods or materials for students of various ability levels.
An Education Bureau spokesman said the results showed that Hong Kong's curriculum reform, with its emphasis on "reading to learn", mathematics development and scientific thinking, had been a success.
"The outstanding performance of Hong Kong pupils in Pisa once again proves that our education is heading in the right direction," the spokesman said.
He said pupils' socio-economic status seemed to have less effect on their performance than in other regions, and that differences in performance among schools was smaller, suggesting they are provided with equal opportunities to receive high- quality education.
Hong Kong joined the ranking in 2000, when the three-yearly study, which began as a comparison between OECD member countries, was opened up to other school systems.