This study examined the effects of a yearlong Mediational Intervention for Sensitizing Caregivers (MISC; Klein, 1992) on: (a) the quality of interactions between rehabilitation day center paraprofessional staff (n =10) and their adult consumers (n =19) with severe intellectual disability (ID) and (b) the consumers’ cognition, autonomy, and behavioral functioning, versus a consumers’ control group (n =13). Regarding the staff–consumer interactions, more mediation of meaning (choice-making), expansion, and competence with explanation and less mediation of physical assistance were observed in the intervention group than in the control group following intervention. On a battery of cognitive measures (n =17), consumers in the MISC group improved their arithmetic skills, temporal concepts, and sequential memory of two digits. Behavioral observations indicated that the MISC group revealed increased positive behaviors, autonomy, and duration of work and decreased verbal and maladaptive behaviors.