The Australian Greens say the My School website isn't as helpful as it should be because it doesn't provide a complete picture of a school.
Greens Senator Sarah Hanson Young says the information is limited, and says the party is concerned it could be used to create league tables.
"(Education Minister) Julia Gillard has said it's all about choice for parents but I challenge her on that," Senator Hanson-Young said in Adelaide.
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"When you look on the website the information is so limited - it's taken from one test that was done on one day of the year, and that's what's being used to inform parents about the way a school is performing.
"It's not particularly helpful, it doesn't give the whole picture of the school, it doesn't tell the whole story.
"The Greens believe we should actually be giving parents more information and the narrow testing that is used to inform the My School website is so limited that it doesn't give parents the information they need, they actually need more information."
Site breakdown
Meanwhile earlier today the site had a malfunction, breaking down after it too many people tried to access it at once.
The controversial website only worked intermittently on Thursday after its launch at 1am (AEDT).
Ms Gillard said within hours some 1.5 million people had tried to access the site, which gives detailed information about literacy and numeracy test results.
"From today, parents, teachers and interested Australians will be able to get on the My School website and see more information about schools than they ever have before," Ms Gillard told reporters in Sydney.
"We know that parents are hungry for this information.
"Indeed they are so hungry for this information that the demand this morning has caused some problems.
"It's a website capable of handling 1.7 million visitors a day and capable of 2350 hits a second.
"Demand in the early hours of of this morning was more than that."
She defended the site against accusations from teaching unions that it could be used to create league tables and unfairly stigmatise poor-performing schools.
Ms Gillard said the website would highlight the good work of top performing schools and that it was better for parents to know and understand why poorly performing schools were struggling.
