A recent survey of California's 7,669 schools - home to one in seven of America's pupils - crystallises what researchers at the universities of California and Southern California have dubbed the "diversity penalty".
Their research found that ethnically and socio-economically homogenous Californian schools stood an 83 per cent chance of meeting targets under the sweeping No Child Left Behind Act. But the odds tumble in schools with the typical racial and parental income mix of America's urban melting pot.
Only 40 per cent of inner-city schools serving students spanning three or more income, ability and ethnic subgroups hit their targets, researchers say. A quarter of schools in California, America's most-populous state, match this description.
Across America, multicultural schools, which must hit a target for each of their subgroups attending, monopolised lists of failing schools. They were listed despite sometimes missing just one or two targets out of 18 or more.
Enacted two years ago yesterday, No Child Left Behind seeks to do exactly that - improve standards for all, including traditionally overlooked minority or deprived groups, hence the multiple targets. Schools missing targets face sanctions culminating in staff dismissals and closure.
Co-author of the California study, Berkeley education professor Bruce Fuller lauded the Act's aims, but said schools faced a "regulatory minefield". He said it was ironic that a Conservative administration dedicated to cutting red tape had brought in such "Orwellian" regulations.
"Britain and America have struggled with the balance between central control and decentralised trust in teachers," he said. "Our study reveals that if you over-regulate you hit perverse... results locally."
A 2002 UCLADartmouth college study had predicted that the most important factor in failure would be schools' racial make-up.
Failure by even supposedly good schools to hit the many targets has embarrassed the President. In 2002, he visited Detroit's high-flying Vandenberg elementary, hailing it as "a school that best demonstrates the philosophy of (No Child Left Behind)."
In November, Vandenberg was deemed failing after missing subgroup targets.