The Uncanny X-Men issue 1

At Xavier's School for Gifted Youngsters in Westchester County, New York, Professor Charles Xavier summons his students telepathically. When the Beast, Angel, Iceman, and Cyclops arrive, he puts them through a series of exercises to hone their mutant talents. Xavier then introduces them to a new student, Marvel Girl, to whom he explains the purpose of his school: his students do receive an education, but they are also the first line of defense against evil mutants.