By AMOS KAMIL From the elevated platform of the No. 1 train’s last stop at 242nd Street, you can just about see the lush 18-acre campus of the Horace Mann School. The walk from the station is short, but it traverses worlds. Leaving the cluttered din of Broadway, you enter the leafy splendor of Fieldston, an enclave of mansions and flowering trees that feels more like a wealthy Westchester suburb than the Bronx. Head up the steep hill, turn left, then walk a bit farther, past the headmaster’s house. From the stone wall that runs along Tibbett...