What group of students was famous for challenging school segregation in the deep south?

Nine black students, who became known as the "Little Rock Nine".

Explanation:

On 17 May 1957, a historic decision was issued by the Supreme court of the United States in the case of Brown v. Board of Education of Topeka that issued segregation in public school as unconstitutional. However, when a group of nine black students enrolled for an all-white school, they were blocked by the National Guard under the direction of Governor Orval Faubus, the event turned to national attention when President called federal troops to escort them into the school.