Australian high school students are up to two school years behind their peers in the world's best performing countries, a major global test of student achievement has revealed.

The results of the OECD's latest Program for International Student Assessment (PISA), released globally on Tuesday night, revealed that not only are the science, reading and maths problem-solving skills of Australian 15-year-olds sliding backwards relative to their international peers, but their skills are declining in real terms.

Australian students were the equivalent of 1½ years behind top-performer Singapore's students in science; a year behind them in reading; and 2⅓ years behind in maths.

Peter Goss from the Grattan Institute said: "Australia is doing worse than Australia used to, and what's disturbing is that this pattern occurs across the board.