edge and professional judgment about how a particular line of inquiry could advance understanding. In areas with little prior knowledge, for example, research will generally need to involve careful description to formulate initial ideas. In such situations, descriptive studies might be undertaken to help bring education problems or trends into sharper relief or to generate plausible theories about the underlying structure of behavior or learning. If the effects of education programs that have been implemented on a large scale are to be understood, however, investigations must be designed to test a set of causal hypotheses. Thus, while we treat the topic of design in this chapter as applying to individual studies, research design has a broader quality as it relates to lines of inquiry that develop over time.

While a full development of these notions goes considerably beyond our charge, we offer this brief overview to place the discussion of methods that follows into perspective. Also, in the concluding section of this chapter, we make a few targeted suggestions for the kinds of work we believe are most needed in education research to make further progress toward robust knowledge.

TYPES OF RESEARCH QUESTIONS

In discussing design, we have to be true to our admonition that the research question drives the design, not vice versa. To simplify matters, the committee recognized that a great number of education research questions fall into three (interrelated) types: description—What is happening? cause—Is there a systematic effect? and process or mechanism—Why or how is it happening?

The first question—What is happening?—invites description of various kinds, so as to properly characterize a population of students, understand the scope and severity of a problem, develop a theory or conjecture, or identify changes over time among different educational indicators—for example, achievement, spending, or teacher qualifications. Description also can include associations among variables, such as the characteristics of schools (e.g., size, location, economic base) that are related to (say) the provision of music and art instruction. The second question is focused on establishing causal effects: Does x cause y? The search for cause, for example,



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