A teacher who is authorized for single subject instruction may be assigned, with his consent, to teach any subject in his authorized fields at any grade level; preschool; kindergarten and grades 1 to 12, inclusive; or in classes organized primarily for adults, and similarly, a teacher authorized for multiple subject instruction may be assigned, with his consent, to teach in any self-contained classroom; preschool; kindergarten and grades 1 to 12, inclusive; or in classes organized primarily for adults; and similarly, a teacher authorized as a specialist teacher may be assigned, with his consent, to teach in his area of specialization at any grade level; preschool; kindergarten and grades 1 to 12, inclusive; or in classes organized primarily for adults.