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Many Americans are of two minds on the issue of affirmative action in college admissions. On the one hand, they recognise that the United States has an egregious history of racial discrimination that needs to be addressed. They also believe that all students learn more—and society benefits—when colleges bring together people of diverse backgrounds.

On the other hand, many Americans are uncomfortable with the idea that the racial box an applicant checks has a large impact on his or her chances of admission. They worry that racial preferences stigmatise beneficiaries, breed resentment, and encourage everyone— including whites—to identify by race. And many other Americans—among them, former President Barack Obama—think it’s unfair when a wealthy African American or Latino applicant receives a preference over a low-income white or Asian student.

Fortunately, an attractive third path is available: giving a leg up to economically disadvantaged students of all races, a disproportionate share of whom are people of colour. Dr Martin Luther King Jr. wrestled with the question of what steps should be taken to remedy America’s history in his 1964 book, “Why We Can’t Wait”. His elegant solution: rather than arguing for or against a Bill of Rights for the Negro, he advocated A Bill of Rights for the Disadvantaged of all races.

This approach has broad appeal with the American public. A 2016 Gallup poll found that while 63% of Americans oppose colleges using race as a factor in admissions, 61% favour consideration of family economic circumstances. The notion that the poor of all races have a special claim is a fundamental tenet of most of the world's great religions. This is consistent with social science research which finds that today, being economically disadvantaged in America poses seven times as large an obstacle to high student achievement as does race.

Some critics complain that King’s class-based approach to affirmative action ignores the reality that race still matters in American society. But King’s policy, which coupled strong enforcement of anti-discrimination laws with class-based affirmative action, does nothing of the sort. The Civil Rights Act and Voting Rights Act are focused directly on racial discrimination in education, employment and voting. And class-based affirmative action is not blind to history.

In building the case for his Bill of Rights for the Disadvantaged, King wrote: "It is obvious that if a man is entered at the starting line in a race three hundred years after another man, the first would have to perform some impossible feat in order to catch up to his fellow runner." But it is precisely because of that history, King argued, that a Bill of Rights for the Disadvantaged would disproportionately benefit black people who “form the vast majority of America’s disadvantaged”. At the same time, it was appropriate for poor whites to benefit, King said, because they suffer deprivation, if not racial discrimination. “It is a simple matter of justice that America, in dealing creatively with the task of raising the Negro from backwardness, should also be rescuing a large stratum of the forgotten white poor,” he wrote.

Since King’s days, researchers have been able to test the viability of socioeconomic preferences in producing racial diversity in the university context. The use of income alone as a measure of socioeconomic status is not optimal because it fails fully to reflect the ways in which structural racism can shape that status. Because of racial discrimination in the housing market, for example, black people are much more likely to live in neighbourhoods with concentrated poverty and have low levels of wealth than do white people of the same income. But if college admissions officers were to use all these elements and weigh admissions by socioeconomic factors, Georgetown researcher Anthony Carnevale and colleagues have found that colleges could achieve racial diversity on selective college campuses while maintaining high academic standards.

Four years ago, in my personal capacity, I signed on to be an expert witness on race-neutral strategies in a lawsuit challenging the use of racial preferences at Harvard University. The litigation produced sophisticated new research that enables a test—using data of actual Harvard applicants—of what would happen if socioeconomic disadvantage rather than race were used in the admissions process.

The simulation in my report begins by turning off a series of preferences that Harvard currently gives to wealthy and disproportionately white applicants. These preferences turn King’s policy on its head by privileging the already privileged. Every year, for example, Harvard admits students through a backdoor channel known as the Z-list, which provides a preference to students on a special “Dean’s Interest” list and other favoured candidates, of whom just 2% were black and 1.2% economically disadvantaged in recent years. Harvard also gives a sizeable preference to the children of Harvard alumni, who are often wealthy and white. According to Harvard’s own analysis, being a legacy candidate increases one’s chances of admission by 40 percentage points, compared with a nine percentage-point boost for low-income students. These types of preferences for the advantaged help explain why Harvard’s student body has 23 times as many high-income students as low-income students.

In addition to eliminating preferences that tend to help wealthy and white students, the simulation in my report replaces racial preferences with a boost for socioeconomically disadvantaged students of all races. The socioeconomic preference we used was about half the magnitude of the preference Harvard provides to recruited athletes. Under the simulation, the share of underrepresented minority students increased from 28% to 30%. The proportion of first generation college students increased from 7% to 25%. And academic preparedness remained superb, with students averaging at the 98th percentile in SAT scores, and posting excellent high school grade point averages. These results were particularly remarkable because Harvard did not provide us with access to wealth data on applicants, which could have increased African American and Latino representation even further.

In the case, 16 selective universities argued that even if socioeconomic preferences produce racial diversity, universities should still be able to use race because “it is artificial to consider an applicant’s experiences and perspectives while turning a blind eye to race. For many applicants their race has influenced, and will continue to influence, their experiences and perspectives.”

But in practice, universities have long relied heavily on race and given short shrift to considerations of economic disadvantage. Harvard’s own analysis found that its preferences for African American students, for example, are about twice as large as their preferences for students from families making less than $60,000 a year. Unsurprisingly, at Harvard, 71% of the black and Latino students come from wealthy backgrounds.

Moreover, the notion that race should be considered in perpetuity—even when socioeconomic preferences can produce racial diversity—ignores the fact that using race to decide who gets ahead has downsides.

King recognised the costs to using racial preferences—particularly for the progressive coalition. King knew that wealthy white interests had long used race to divide working-class whites and blacks from joining forces. He did not want to further that goal by embracing racial preferences. King wrote to an editor of “Why We Can’t Wait”: “It is my opinion that many white workers whose economic condition is not too far removed from the economic condition of his black brother, will find it difficult to accept a ‘Negro Bill of Rights,’ which seeks to give special consideration to the Negro in the context of unemployment, joblessness, etc and does not take into sufficient account their plight [that of the white worker].”

In a 1987 address at Harvard University’s chapel commemorating King’s life, King’s close advisor Bayard Rustin emphasised the division caused by racial preferences. “Any preferential approach postulated along racial, ethnic, religious, or sexual lines will only disrupt a multicultural society and lead to a backlash,” he declared.

Universities have taken a very different path from the one King and Rustin advocated, which demagogues on the right have brilliantly exploited. Racial preference programmes surely help explain why 60% of white working-class Americans say that “discrimination against whites has become as big a problem as discrimination against blacks.”

More than 50 years ago, King was right to suggest an inclusive path for the country that brought working-class people of all races together. In the age of Donald Trump, when division is being amplified daily, it is urgent to return to a policy that lifts up forgotten disadvantaged people of all races.

Richard D. Kahlenberg is the author of “The Remedy: Class, Race and Affirmative Action” and an expert witness in Students for Fair Admissions v. Harvard