Three nonprofessionals, including those with limited education and advanced age, received training to become effective behavior modification agents (therapists). Each was then individually observed and videotaped in his work with a retarded child. Therapists' performances were not adequate for effecting the desired changes in the childrens' behavior. A subsequent videotape-feedback training program resulted in improvements in both therapist and child behaviors. These were maintained even after the training condition was withdrawn. Based on these positive results, 3 mothers were similarly trained to work with their own young children. A major point revealed in this investigation is that it does not suffice merely to present the nonprofessional therapist with a behavior modification program and an injunction to carry it out. Explicit, detailed training and close scrutiny are required for providing a wide range of nonprofessionals with behavior modification skills. (Author/TL)