To study the effects of the sharing of facilities between a regular high school and a school for senior trainable mentally retarded (TMR) students, observations were made of the interaction between the two schools, of the administrative model of semi-integration, and of aspects of the behavior of the retarded students compared with similar students in a segregated TMR school. The program discussed is a semi-integrated school (designed to share available space) as opposed to semi-integrated education (designed for educational outcomes). There was no evidence that the semi-integrated school is inferior to a segregated setting in terms of academic, social, or self-concepts of the retarded students, or that regular students accrued benefits in learning to live with handicapped people. Communication between the two teaching staffs is essential to the success of, but precluded by the structure of, the semi-integrated school model. Where future semi-integration is undertaken because space is available, the project should be jointly planned by the teaching staffs involved, with orientation of all other people affected. Semi-integration of large numbers of TMR students is not recommended at the secondary level. The semi-integrated schools can incorporate the aims of semi-integrated education. (Author/IRT)