The answer to this is that the Brown case overturned a case called Plessy v. Ferguson. This case was decided in 1896.
The Plessy decision was the one in which the Supreme Court laid out the doctrine that "separate but equal" facilities for people of different races did not violate the 14th Amendment. The Court argued that the 14th Amendment said that blacks and whites had to be treated equally, but not that they had to be treated equally in the same train cars. So long as the train cars (or, by extension, the schools) were equal, the fact that they were separate was not important.
In Brown, the Court held that separate schools for the races were inherently unequal. By making this ruling, it effective overruled Plessy.
Brown v. Board of Education overturned the case of Plessy v. Ferguson.
In 1896, the decision of Plessy v. Ferguson upheld state racial segregation laws for public facilities with a vote of 7 to 1. The majority opinion in this case, which was written by Justice Henry Billings Brown, favored a doctrine of "separate by equal." This case was brought to the US Supreme Court after Homer Plessy, an individual of mixed race, refused to vacate a "whites-only" railway car. This ruling was predicated on the idea that because the whites-only and blacks-only railway cars were inherently equal in terms of the quality of their facilities, there is no issue with maintaining racial separation. This ignored the fact that most other public facilities designated for blacks did not meet the standard of quality reserved for the whites-only facilities.
Thus, the 1954 decision of Brown v. Board of Education of Topeka overturned the Plessy ruling by declaring that the segregation of public schools was unconstitutional.
Brown V. Board of Ed , its ruling reversed the principle "separate but equal" established in Plessey V. Fergusson. It declared racially segregated public schools inherently unequal.
The case of Plessy v. Ferguson was overturned in 1954 by Brown v. Board of Education.
In Plessy v. Ferguson (1896), the U.S. Supreme Court decided that a Louisiana law mandating separate but equal accommodations for blacks and whites on intrastate railroads was constitutional. This decision provided the legal foundation to justify many other actions by state and local governments to socially separate blacks and whites.