Grammar schools continued to admit many pupils from affluent backgrounds despite the cancellation of transfer tests in 2021.
That is one of the key findings from a new study by the Centre for Research in Educational Underachievement (CREU) at Stranmillis College in Belfast.
It said non-grammars still had more pupils from disadvantaged backgrounds or with special educational needs.
The transfer tests were cancelled in early 2021 due to the Covid pandemic.
"The social composition of grammar schools thus remains very positively skewed towards children from more affluent postcodes," the study said.
"We have a grammar school sector in Northern Ireland which, consistently, has very few children from the most socially deprived areas, very few children entitled to free school meals, very few children with special educational needs and very few newcomer children."