Uncanny X-Men #3 (Marvel, 1964 — Cover A)

The story opens with the X-men training in the schools gymnasium. Today Scott Summers is practicing the speed at which he can blast bean bags that are being launched at him by the Beast. The other boys are involved with some one-upmanship and roughhousing until Professor X calls them to order. Jean's task is to move a block of wood through a series of obstacles as quickly as possible. Their training is interrupted when Professor X detects the presence of another mutant nearby.