This study aimed to draw upon a sociocultural perspective for elucidating the process and outcome of peer learning interactions between young adults with serious learning disabilities. A heterogeneous group of ten young adults between ages of 18 and 27 participated in the year-long cognitive program based on the principles of Feuerstein's theory of mediated learning and Instrumental Enrichment (IE) program. Six of the participants had Down's Syndrome and the others suffered from various disabilities including brain damage, and cerebral palsy. The program included 178 hours of IE cognitive intervention. The peer mediation process was supplemented by an additional emphasis upon collaborative group discussion at the end of every session. A post-positivist research design similar to the design experiment of Russian Vygotskians was employed in order to evaluate both the process and the outcomes of the intervention programme. The results show that after one year the participants' learning self-concept was well above average. Moreover, their reflections about how they had changed as a result of their involvement in the programme and their descriptions of what was required to provide effective mediation demonstrated deep levels of cognitive, emotional and social development.