An Oireachtas committee has heard that a past pupils admissions provision is dangerous, discriminatory and should be discontinued.
For the past two admissions cycles, schools have been allowed to ring-fence a quarter of their places for children and grandchildren of past pupils.
This is "the epitome of promoting intergenerational disadvantage", the head of Barnardos said, while the Children's Ombudsman insisted that "we need to make sure that we stamp it out - now".
Dr Niall Muldoon also criticised the Joint Managerial Body for failing to provide figures on the impact of the measure.
"That's crucial. We should have those figures to hand," he said.
The Joint Committee on Education is continuing its consideration of the Labour Party's Education (Admission to Schools) Bill which would remove the past pupils provision.
Áine Lynch, CEO of the National Parents Council (Primary), cautioned that the provision sets a "dangerous" tone for society.
She said it endorses discrimination against children, where already "the odds are against them", and tells them that "your history can define your future".
And "[what] happens in a school shapes the communities around them", Ms Lynch cautioned.
The CEO of Barnardos told the committee that education offers children a "way out" of often severe disadvantage.
Suzanne Connolly said many children that Barnardos helps are caught in "complex and frequently chaotic circumstances".
She warned that the past pupils provision effectively blocks that educational avenue of escape, and it contravenes the UN Convention of the Rights of the Child which guarantees equal access to education.
Dr Muldoon agreed, saying those who risk being "particularly disadvantaged" are children whose parents are immigrants or have disabilities, and Traveller children.
The Ombudsman warned that the measure "contributes to a continuing cycle of disadvantage".
He said that by giving one group "preferential access to schooling", the State is failing those who are being denied that benefit.
Dr David Doyle, associate professor in Law, Maynooth University, said that overall, the 2018 act - which introduced the past pupil provision - was "a step in the right direction".
But the past pupils provision is "fundamentally unjust" and "inherently discriminatory" he said, adding that it is "virtually impossible for certain minority groups to meet the [past pupil] criteria".
That is the definition of discriminatory, Dr Doyle concluded.
Sinn Féin TD Donnchadh Ó Laoghaire said that John Stokes' experience in Clonmel, Co Tipperary, was reason enough to have the provision removed.
The boy from the Traveller community lost a Supreme Court challenge he brought against the Christian Brothers High School for refusing him admission in 2009.
The school had a policy of giving preference to the children of past pupils.
Deputy Ó Laoghaire noted that this had occurred before the past pupils provision was given the protection of law.
Now, the prospects for someone in similar circumstances getting fair treatment were even more remote, he said.
