Below, I have published how children who lived outside London at the age of 11 went on to do in their GCSEs (using our usual point score) at the age of 16.
I have divided this set of pupils twice: first, by whether they had moved into London by the age of 16 or not and second by how well they did in standardised tests at the age of 11.
You can see a clear advantage to moving into the city. Children who moved to London outperformed those of similar ability who remained outside the capital.
Conversely, what happened to children who were in London at 11 if they subsequently left the capital?
Staying in the city confers a big advantage.