Plessy v. Ferguson ushered in an era of increased discrimination towards blacks. The decision's "separate but equal" doctrine provided justification for segregation in public facilities across the country, including schools. The doctrine stood almost unchallenged for nearly fifty years, until a series of decisions questioning the constitutionality of segregation in institutions of higher learning.
One of the early segregation cases was Sweatt v. Painter. Herman Sweatt was a black who wanted to attend the University of Texas Law School. The law school denied him admission solely because of his race. Texas had set up another law school for blacks, but Sweatt argued that the black school was not equal to the white school. Indeed, it wasn't; it was not as large and, because it was newer, it did not have as good a reputation. Sweatt took his case to the Supreme Court. In 1950, the Court ruled in favor of Sweatt and forced the University of Texas Law School to admit him.
A slightly different segregation case was McLaurin v. Oklahoma State Regents for Higher Education. Oklahoma State University admitted G.W. McLaurin, a black citizen of the state, because the black state colleges did not have comparable programs. The university, however, forced McLaurin to sit in isolated seats in the classrooms, library, and cafeteria.  McLaurin argued that this policy was unconstitutional, and the Supreme Court agreed in a unanimous decision.
These two decisions had a substantial impact on later segregation cases. Speaking for a unanimous Court in Sweatt v. Painter, Chief Justice Vinson wrote:
"With such a substantial and significant segment of society excluded, we cannot conclude that the education offered [Mr. Sweatt] is substantially equal to that which he would receive if admitted to the University of Texas Law school." 
In a New York Times article on the decision, Benjamin Fine noted:
"[Chief Justice Vinson's] statement was immediately seized upon by those who are opposed to the segregation policy. They saw in it an opening wedge that might lead to the final and complete overthrow of all educational segregation in the South. For, they argued, under this interpretation, it would be utterly impossible for any Negro college or university, no matter how adequately equipped or financed, to provide 'equal' opportunities to the Negro student." 
This proved to be the case in later Supreme Court decisions, including Brown v. Board of Education. Sweatt and McLaurin contributed to the Brown decision by providing an early precedent saying that "separate but equal" was not neccessarily true in education. They also provided a different interpretation of the Fourteenth Amendment to the Constitution than the one used in Plessy v. Ferguson, which served as the precedent until these decisions. In Plessy, the Court ruled that the Fourteenth Amendment did not require "social comingling of the races;" in McLaurin, it ruled that isolating McLaurin from the rest of the student body because of race denied him equal protection of the law and therefore violated the Fourteenth Amendment. Sweatt took into account both tangible and intangible inequalities between the white and black law schools; Plessy did not consider the intangible factors. By providing a newer interpretation of the Fourteenth Amendment than that of Plessy, Sweatt v. Painter and McLaurin v. Oklahoma State Regents for Higher Education paved the way for later Supreme Court decisions on desegregation of public schools.