Read for diploma of policy and program evaluation. They summarize realistic evaluation in one (run-on) sentence:
The perspective begins with a theory of causal explanation based on generative principles which supposes that regularities in the patterning of social activities are brought about by the underlying mechanism constituted by people's reasoning and the resources they are able to summon in a particular context, which gives research the task of testing theories of how program outcomes are generated by specific mechanisms and contexts, a task which involves making inter- and intra-program comparisons in order to see which context-mechanism-outcome configurations are efficacious, which thus sees programming as an attempt to embody knowledge which has thus identified what works for whom in what circumstances, knowledge of which accumulates over successive trials of a program and from other forms of empirical research, providing policy makers with families of theories specifying typologies of successful context-mechanism-outcome combinations, knowledge of which is promulgated by a teaching and learning process in which the stakeholders' fragmentary expertise is marshalled by the researcher.