To date, hardly any evidence is available on the quality of adult education programs for vulnerable adults. Evaluation instruments or models mostly focussed on regular education and less on programs of adult education aiming to enhance social inclusion. This study presents a first exploration of the construct validity of a newly developed instrument, called the SIT-instrument (social inclusion after transfer) for the evaluation of educational programs for vulnerable adults and their impact on increasing social inclusion. The sample consisted of 308 respondents belonging to the target-group of vulnerable adults. The results of the validation study indicate a reliable instrument consisting of elements of a learning-environment for "vulnerable" adults influencing 4 specified categories of social inclusion. (Contains 5 tables.)