They also claim that effectiveness studies ignore the processes in educational institutions and forget that the research is focusing on a school or schools at a certain point in time. Harber and Davies (1997) quote the work of Harbison and Hanushek(1992) who, in a large-scale study, showed the difficulty in identifying teacher effectiveness through quantitative measures only: ‘the choice of quantitative differences between teachers such as their years of formal education ignores other far more important aspects of their “art” (Harber and Davies, 1997, p.3)