Nearly a quarter of London secondary pupils travel to schools outside the borough they live in.
But there is huge variation among the capital's 33 education authorities in cross-border movement, say figures from the Department for Education and Skills.
Overall they show that of the 378,252 state-funded secondary pupils living in London in 20034, 86,325 or 22.8 per cent of them went to school outside the local authority area they lived in.
Kensington and Chelsea had the biggest proportion of incomers, with nearly six in 10 pupils in its secondaries coming from outside the borough. But, apart from the City of London which has no secondary schools, it also had the largest exodus with 57.2 per cent of its 2,871 resident secondary pupils, going to school elsewhere.
At the other extreme was Tower Hamlets with only 7.3 per cent of its 11,583 resident pupils crossing its borders, closely followed by its east London next-door neighbour, Newham with just 8.7 per cent.
The problem of pupils "criss-crossing London on hour-long journeys" was identified by the Government when it launched its London Challenge strategy to raise secondary standards in 2003. It quoted research showing fewer parents in London apply to their nearest state school, choose a school in their borough, or get into the school they prefer.
The DfES attributed this movement partly to decisions by the old Inner London Education Authority to establish schools in one borough to serve another and the closure of poor performing schools in some areas.
But it also noted a lack of parental confidence in local schools. Tony Blair illustrated the point by opting for London Oratory school in Fulham for his eldest sons instead of local Islington comprehensives.
In 20034 the parents of 3,077 pupils or 38.8 per cent of those living in Islington followed the Prime Minister's example.
Highest percentages of state pupils leaving their borough to go to school
City of London* 100
Kensington Chelsea 57.2
Lambeth 55.9 Hammersmith Fulham 44.8
Hackney 42.6 Islington 38.8
* City of London has no secondary schools Highest percentages of pupils from other boroughs
Kensington Chelsea 59.4
Hammersmith Fulham 51.8