The Fifth Squad said Delano White, 17, of 18 Cedar St., was arrested at his home without incident at about 12:40 p.m.
At about 3:30 p.m. on May 29, police said White pushed a 13-year-old boy to the ground on Baylis Avenue in Elmont. White, displaying a knife, then took the boy's backpack and removed an iPhone from it, police said.
He then fled on foot, police said.
White is scheduled to be arraigned Wednesday on a charge of first-degree robbery at First District Court in Hempstead.