The correct answer is: Sweatt struck down “separate but equal” graduate and professional schools. Brown struck down “separate but equal” public schools.
Indeed, Herman Marion Sweatt, an African-American student tried to enroll in the University of Texas’ Scholl of Law in 1945. His entry was refused due to the fact that integrated education was contrary to the state’s Constitution. He filed a lawsuit against the decision and the state responded by building a new segregated Law School in Houston Texas for African American students. He was able to win the case in the US Supreme Court because his attorneys demonstrated that the proposed new facilities were of a much inferior quality than the ones in the University of Texas. They were also underfunded, understaffed and its library was much smaller. This was found to violate the separated but equal principle.
The same rationale was applied in Brown v. Board of Education in 1951. 13 African American families filed the lawsuit because their children had been refused admission in white public schools which were located very close to their homes. It was proven by their litigators that their black schools were not only of considerable lower quality but were too far from their homes.