The correct answer is: "Plessy v. Ferguson"
Plessy vs Ferguson was a landmark decision enacted by the US Supreme Court in 1896, which legimitized the existence of segregated public education facilities as long as these were equal in quality. It actually introduced the principle of "separate but equal".
In the Plessy v. Ferguson the justices had considered that, as long as equal quality was provided, segregation was not violating the Equal Protection Clause included in the 14th Amendment to the US Constitution. Therefore, segregation was not contrary to the US Constitution and therefore legitime. Fortunately, the Supreme Court in 1954, in the case of Brown v. Board of Education understood it differently, and dismantled segregation forever.