A thermoplastic composition includes a poly(arylene ether) and a poly(arylene ether)-polysiloxane block copolymer. The thermoplastic composition is prepared by a method that includes oxidatively copolymerizing a monohydric phenol and a hydroxyaryl-terminated polysiloxane. The method is simpler than prior methods of preparing poly(arylene ether)-polysiloxane block copolymers by linking pre-formed poly(arylene ether) and polysiloxane blocks. The method is also produces greater incorporation of polysiloxane into the poly(arylene ether)-polysiloxane block copolymer than prior methods of copolymerizing monohydric phenols and hydroxyaryl-terminated polysiloxane.