Singapore's 15-year-olds once again emerged among the top performers in the Programme for International Student Assessment (Pisa) test conducted last year. The results released at 6pm on Tuesday ranked Singapore students second in mathematics and third in science and reading. In the previous Pisa conducted in 2009, students here were placed second in mathematics, fourth in science and fifth in reading. A total of 65 countries and economies took part in the latest study.

Singapore students performed even better - coming in No 1 among the 32 education systems which opted to participate in the computer-based assessments of mathematics and reading.

This is the second time that Singapore has participated in the study which is conducted once every three years by the Organisation for Economic Cooperation and Development (OECD). Rankings are based on a country's average score in the test. Shanghai, which is also taking part for the second time, came in tops in all three categories. Asian cities including Hong Kong and Japan hogged the top five positions. The only exception was Finland, which came in fifth in reading and sixth in science.

Pisa 2012 also showed that Singapore helped to level up the academically-weaker students, while sustaining the strong performance of the academically-stronger students. The proportion of weak performers dropped, while the number of top performers increased compared to 2009.

The OECD chose to assess 15-year-olds as they are nearing the end of secondary education. In Singapore, a total of 5,369 randomly-picked students, mainly from Secondary 3 and 4, from all 166 public secondary schools and 177 students from six private schools including international schools participated in the study.

Each student had to complete one test booklet of multiple-choice and open-ended questions, which required them to use their knowledge and skills in mathematics, science and reading to solve problems.