Sex typing among preschool children was investigated by means of a complete experimental design to test which factors maintain sex-typed behaviors, to test whether sex-typed behaviors are learned, and to reduce sex typing. The complete experimental design, it is maintained, allows investigators to focus on the consequences of sex typing rather than to accept the assumptions which restrained earlier research such as biological determinism, normal gender identification, adult roles and aspirations, and psychological adjustment. Findings indicate that cuing and labeling by teachers, social reinforcement (that is, attention and praise), teacher modeling, and even the physical location of the teacher in the classroom can reduce or eliminate sex typing of activities in which boys and girls participate, can influence independent activity, and can more than double the amount of cooperative play between the sexes. It is argued that reduction of sex typing has been extremely rapid, but generalization and maintenance has been minimal and that stimulus discrimination explains these effects. (Author/DB)