ERO reports published from the beginning of Term 4 onwards will not have decile ratings included.
New Zealand Education Institute president Ian Leckie said he was surprised the ERO had decided that decile ratings did not provide parents with meaningful information.
He said parents must be provided with clear information about the social and economic contexts in which schools operate so they can make a fair assessment of the effectiveness of schools.
"Decile ratings are clearly crude tools, but if ERO is to remove these ratings, it should still give parents information about the socio-economic context in which a school operates," he said.
"Poverty, ill-health and poor housing have significant impacts on whether children are ready and able to learn.
"ERO cannot pretend these out-of-school factors do not affect student achievement and therefore whether a school is perceived as effective or not."
Mr Leckie said neither the ERO nor parents should be kept ignorant of the real-world challenges faced by schools.
Earlier this month, Education Minister Hekia Parata announced that the Ministry of Education would publish achievement data on the ministry's website.
The site will not rank schools in league-table fashion but will show achievement data in regions and how individual schools are performing against national standards.