Exam fatigue has been blamed for Junior Cert students performing badly in an international test.
Irish 15-year-olds were tested in March when many were in the middle of orals and practicals in the run-up to the Junior Cert in June.
By contrast, British students were tested in the autumn, which is well away from student exams.
The Programme for International Student Assessment (PISA) is an international survey of student achievement in reading, maths and scientific literacy across 60 countries in the developed world, and is carried out every three years.
A detailed study of PISA 2009 attributes the decline partly to the timing of the test in the run-up to the Junior Cert.
About two-thirds of those who took the PISA 2009 were sitting the Junior Cert.
But there was also an acceptance that standards in Ireland had dropped.
A dramatic decline in reading achievement left Ireland performing at only average level in the developed world, while maths performance was also down.
Governments put a lot of store in PISA for what it tells them about how students compare, and it is watched carefully by multi-national employers making decisions about where to locate.
According to the analysis, Irish students "did not engage in, or try as hard", in PISA in 2009 compared with previous tests.
Based on the initial findings, Education Minister Ruairi Quinn last year announced a new literacy and numeracy strategy.
Since 2000, there was an increase from 32pc to 44pc in the number of students who don't read for enjoyment.