This paper provides practical guidance for researchers who are designing and analyzing studies that randomize schools--which comprise three levels of clustering (students in classrooms in schools)--to measure intervention effects on student academic outcomes when information on the middle level (classrooms) is missing. This situation arises…

This is an introduction to a set of four papers in the field of evaluation research. A main theme in these papers is the recognition that evaluation research is not a pure objective scientific self-standing activity, but one that interacts within a context and is influenced by the interchanges. (LMO)