ABSTRACT
This chapter addresses the multiple kinds of data and evaluative claims at work in Duncan's discourse, and it explores the kinds of justification that are both possible and requisite for each. The analysis of achievement data promises to solve the problems inherent in both types of ordinary appeals cited above. In his many speeches touching upon or directly dealing with the use of data, Duncan treats the availability of longitudinal data as offering something profoundly new to the education profession. The author have seen that both of the criteria appeals discussed above require a certain acceptance or agreement on the part of those to whom educational quality is reported, that is, a certain sharing of forms of life is simply assumed. Achievement data enters in response to the inadequacies of each type of ordinary appeal. Duncan's valorization of student achievement data responds to precisely this slipperiness.
