Research for the Sutton Trust suggests state schools in England take twice the rate of smart, poor pupils compared to grammar schools. The report also suggests that state faith schools take fewer poorer pupils compared to other state secondaries.
The government said the mandatory admissions code introduced last year outlawed unfair admission practices.
The researchers based at Durham University analysed the pupil characteristics of every child who began secondary school in England in 2001.
They found that about 2% of grammar school pupils were from low income families - on free school meals, compared to 12% of pupils at non-grammar schools. This is largely because those attending grammar schools have to pass an academic test and only one in 20 pupils among the top performing pupils are on free school meals, they said.
However, in grammar schools only 2% of the top achievers were on free school meals, compared to 5.5% for non-grammar schools. They also compared the rate of pupils on free school meals at a school with that of the areas from which they drew their pupils.
