Rosina you are right. The thing is, it proves that the good results are not to do with the school itself, so people who are voting for, or advocating, a system of Grammar Schools can be told it has been scientifically proved that they are not necessary since they make no difference.
There is such a big urge to bring back Grammar Schools that this research, proving the obvious, but so as to make it irrefutable, is essential.
Please, everyone, do all you can to stop this Grammar School resurgence. It is not a return of good schools. The research demonstrates this. It is an elitist system to give privilege to those already in a favourable situation. It encourages the wrong kind of competition. This competition, we have seen in other research, begins with parents looking for aggressively "academic" teaching (the child is schooled to sit at their desk all day writing and doing rote learning) from the age of 3!
A Grammar School system condemns 90% of our children to being labelled as "failures". Whatever you say, try asking a child who has not been offered a much prized grammar-school place, what they did at 11+ and they will say "I failed".
Good schools are made up of all-comers who are well taught and where opportunities are available and aspirations are high.
I know this. I was involved with both teaching, school inspection and research into educational assessment. Also two of my daughters went to a grammar school, the third was about to go, we moved, she went to a brilliant comprehensive where she did more, was given wider experiences and gained the same A levels and went to a top university.
The divisive and elitist system of grammar schools harm our educational system and our children, including the children attending the grammar school.