One million school students sat Australia's first national standardised tests today, amid concerns about the system.

Students in years 3, 5, 7 and 9 will sit the literacy and numeracy tests over the next three days. This morning's first test was writing.

Federal Education Minister Julia Gillard said the results will enable parents and teachers to see how their students perform in key learning areas in relation to the rest of the country.

"It's important for government and it's important to teachers because it obviously shows which schools and which students are in need for additional assistance," Ms Gillard told ABC Radio.

Queensland Education Minister Rod Welford said parents should encourage their children ahead of the tests, which will cover subjects they regularly learn in class.

"The important thing to note is that for students, teachers and schools there will be very little change from the former Queensland testing arrangements," Mr Welford said.

"The main factor that has changed is that students from across the country will sit the same tests at the same time."

NSW Premier Morris Iemma said the "mammoth undertaking" of testing nationwide was only possible thanks to cross-government cooperation.

But in some states or territories — including the Northern Territory and South Australia — union teachers are opposing the test, or refusing to take part in protest against their governments over school resourcing or teacher wages.

In Victoria, the education union called off plans to boycott the test after securing a $2 billion wage deal with the Brumby Government last week.

Others doubt whether the program will provide valuable information to parents.