Kushner was born in Manhattan, New York, the son of Sylvia (née Deutscher), a bassoonist, and william David Kushner, a clarinetist and Conductor. His family is Jewish, descended from immigrants from Russia/Poland. Shortly after his birth, Kushner's parents moved to Lake Charles, Louisiana, the seat of Calcasieu Parish where he spent his childhood. During high school Kushner was active in policy debate. In 1974, Kushner moved to New York to begin his undergraduate college education at Columbia University, where he received a Bachelor of Arts degree in Medieval Studies in 1978. He attended the Tisch School of the Arts at NYU, graduating in 1984. During graduate school, he spent the summers of 1978–1981 directing both early original works (Masque of the Owls and Incidents and Occurrences During the Travels of the Tailor Max) and plays by Shakespeare (A Midsummer Night's Dream and The Tempest) starring the children attending the Governor's Program for Gifted Children (GPGC) in Lake Charles.