The results were released in the three-yearly Program for International Student Assessment (PISA).
More than half a million 15 year-olds from 72 countries took part in the report, including 14,000 Australian children.
The tests, conducted by the OECD, have become increasingly influential on politicians who see their countries and their policies being measured against each other in these global school league tables.
Asian countries continue to dominate, with Singapore topping the list.
Chief executive of the global teaching organisation, Teach First, Brett Wigdortz says the results are unsurprising.
"It shows that there are a few countries that have real global leading education systems and they are spread around the world - Singapore, South Korea, Canada, Finland, Estonia - who are doing really fantastic work with their education systems, then you have some systems that are doing well and England is one of those that's doing well, but not as good as it needs to be, and then you do have systems that are not really providing great education for their young people and really need to improve."
Australia is above the OECD average, but sits equal 10th in science, equal 12th in reading and equal 20th in maths.
It was outperformed by Finland in all three PISA areas, by Vietnam in Science and by Slovenia, again, in maths.
It found that:
- Australian science students are now seven months behind where they were in 2006,
- an Australian maths student is a year of schooling behind where they were in 2003 and
- Australian students' reading abilities have also dropped by a year since 2000.
Dr Jennifer Buckingham, from the Centre for Independent Studies, has told the ABC there's a lot to learn from Singapore.
"Singapore is obviously a very different demographic and social context to Australia, and so I think it's really important to be careful not to make simplistic country comparisons, but Singapore has been doing really well in PISA for many years and has been right near the top. Singapore has a really specific focus on developing teacher expertise and puts a lot of investment, a lot of effort into recruiting the highest calibre people to go into teaching, and also then training them and spending a lot of time developing them as they progress through their career. "
Last week's Trends in International Mathematics and Science Study (TIMSS) also showed Australian students in the middle of the pack after 20 years of testing.
Federal Education Minister, Simon Birmingham, says the results are worrying.
"In some ways this gives us greater cause for concern. The TIMSS report last week focused on our international performance in maths and science showed us slipping in the rankings. This report shows performance across maths, science and reading, performing in real terms. So Australian 15 year-olds in 2015, when this report was undertaken and assessed, were performing at a lesser standard than earlier generations of Australian students. Go back to 2003 and in fact some students are performing around one year below those students in 2015 in terms of their academic accomplishments."
Dr Jennifer Buckingham says both result sets show Australia's education system has serious deficiencies.
"One of the things that comes through quite clearly when you look at multiple comparisons of countries over multiple years is a relationship between certain styles of teaching and student performance. So over the last few cycles of PISA we have seen a relationship between teacher directed styles of classrooms pedagogy, and that means explicit instruction in really core concepts. Those teachers deliberately and methodically lead students through what they need to learn, checking for their understanding lots of monitoring and assessments that sort of thing, whereas inquiry-based approaches have a negative association with performance in PISA. Inquiry-based approaches have been the favoured approaches in Australia for the last decade or more."
Minister Birmingham concedes the education system requires change to improve the outcomes for students.
"We should recognise that our system still performs above the OECD average. So first of all, it's not a crisis point but it is a warning signal that we are in a downward trajectory and trend that we need to work to reverse. The factors influencing that, some of them would be the home environment and some may be technology, but the things within our control in terms of how we prepare and train our teachers and where we intervene at the earliest stages and the levels of ambition set within the schools - they are the factors that the State and education ministers can work on with me and focus on for the future."
