Teaching unions in Wales have criticised "insufficient detail" in school reforms proposed by Education Minister Leighton Andrews.
However, at a conference in Cardiff, he insisted parents had a right to information about schools' performance.
Mr Andrews said parents' demand for transparency would not go away.
Earlier the National Union of Teachers (NUT) said the plans were "full of vague notions and ideas that do not have enough meat on them".
Speaking before Mr Andrews' speech on Monday afternoon, David Evans, secretary of NUT Cymru, said he opposed in principle plans the grading plans.
The union feared a return to league tables which were abolished in Wales in 2001, he said.
Dr Phillip Dixon, director of the Association of Teachers and Lecturers (ATL), said this proposal was of "grave concern" and he would be urging that schools' grades are not published nationally.
The minister insisted the new system will be different as schools will not be judged solely on GCSE performance.
BBC Wales asked all six teaching unions whether they supported plans for school reform, which the minister delivered as 20 areas for immediate action in a speech earlier this month.
The Association of School and College Leaders said grading schools could do "more harm than good" while Welsh teaching union UCAC opposed the minister's proposal to close failing schools.
UCAC's policy officer, Rebecca Williams, said it was difficult to imagine a situation in which a school is irredeemable.
"It may need a change of leadership or other serious changes, but closing a school is a drastic and complicated business," she said.
However, unions supported some of the proposals.
The ATL said plans to tackle poor behaviour in the classroom with more training for newly-qualified teachers were "especially welcome".
UCAC said it was pleased to see a renewed emphasis on pupils' literacy and numeracy, especially in the early years.
The minister is proposing national reading tests for six year olds after a report from the school inspectorate Estyn found that 40% of Welsh primary school pupils had a reading age below their actual age.
Unions met Mr Andrews last week, but there was nevertheless a unanimous call for further details.
Iwan Guy, acting director of the National Association of Headteachers Cymru, said there was "confusion" about the plans, while David Evans from NUT Cymru said there was "insufficient" information in support of the proposals.
Before his speech Mr Andrews said the teaching unions had an important role to play in the changes.
"I had a very good discussion [with unions] and I have to say that they were far more muted in their comments at that meeting than they now are in their press statements.
"I've made it clear that we need to see a step-change in performance in Welsh schools.
"But we have to raise school performance and schools will be graded by local authorities as they are by our education inspectorate Estyn and I believe parents and pupils will welcome such transparency."