Texas is a complicated place. Once part of Mexico, later racially segregated and now an oil-fuelled American boom state, it is a human patchwork quilt of all colours and means.
So when its public universities were forced by court order to stop giving preference in admissions to non-whites on the basis of their race, they needed some other way to reflect the state's diversity.
What Texan policymakers came up with was legislation drily called House Bill 588 but more commonly known as the "Top 10 Per Cent Rule".
It required public universities to take the top 10 per cent of students from every state secondary school - white, black, Hispanic, rich, poor, urban, rural or suburban - thereby guaranteeing a student body that reflected the population.
More than 10 years later, the idea is spreading as a way of ensuring fairness even when the quality of secondary education varies widely.
The University of California next year will begin a scheme to accept the top 9 per cent of secondary school graduates. The Florida system guarantees admission to the top 20 per cent.
Momentum behind the idea is also picking up internationally, with universities in France and the Republic of Ireland considering it.
For example, Patrick Prendergast, the provost-elect of Trinity College Dublin, has proposed that as a means of encouraging socio-economic diversity, Trinity should accept the top 10 per cent of students from all state schools in and around the city rather than relying on examination results that favour private fee-paying schools.
Seven such schools sent 375 students to Trinity this year, while only 80 came from 53 state schools.
Trinity has hitherto failed to meet its goals for admitting low-income, disabled and mature students, so the proposal could help it to meet some of the targets. But Professor Prendergast declined to discuss the plans until he takes office in August.
Necessary tweaks
But even as others try to emulate the Top 10 Per Cent Rule, Texas has been forced to make adjustments to it. The approach has not achieved the racial balance that was hoped for and parents complain that it discriminates against high-achieving students.
"It has worked almost too well," said Augustine Garza, deputy director of admissions at the University of Texas.
Within a few years of the rule being enacted, 81 per cent of the students at the flagship University of Texas at Austin were being admitted according to its auspices, freezing out other qualified applicants.
"You quickly see the dilemma that we faced," said Mr Garza. "We saw so many kids applying and we had to say yes. We were filling the whole class with top 10 percenters.
"But we had tremendously talented students in the 11th percentile, 15th percentile, 25th percentile, and we couldn't accept them because there simply wasn't room."
So the state legislature has modified the plan. Effective this year, it allows Texas to limit the proportion of students admitted under the Top 10 Per Cent Rule to a maximum of 75 per cent of enrolment.
The university now accepts the top 1 per cent, then the top 2 per cent, then the top 3 per cent and so on until the ceiling is reached - this year, when it hit the top 8 per cent.
Top 10 disappointments
But despite the modifications, the plan has not maintained the racial diversity that existed under the affirmative-action policy that preceded it.
Non-whites turned out not to be as widely represented as expected among the top 10 per cent of even urban schools.
One reason for that, a study this year found, is that other students, many of them white, have been transferring to lower-quality schools in order to graduate in the top 10 per cent.
A Princeton University sociologist, Marta Trenda, has found that the rates of admission for blacks and Hispanics have actually fallen since the rule was adopted.
Although the top 10 per cent of students are guaranteed admission to public universities, they are not necessarily promised financial aid.
Florida's so-called Talented 20 programme seeks to address this problem. It guarantees not only admission for the top 20 per cent of secondary school graduates, but also puts them at the front of the line for financial aid.
Critics say that in the rush to increase non-white and low-income enrolment, laws such as the Top 10 Per Cent Rule simply discriminate against another group: well-off, high-achieving students in good private and suburban public schools.
For university leaders, the challenge is to improve the chances of the disadvantaged, without disadvantaging others in the process.