1. Replicate and generalize across studies.

  2. Disclose research to encourage professional scrutiny and critique.

The application of these principles to questions about teacher preparation poses particular conceptual and empirical challenges:

  • There are no well-formed theories that link teacher preparation to student outcomes.

  • The complex nature of schooling children makes it difficult to identify empirically the role of teacher preparation among the many intertwined influences on student outcomes.

  • The use of strict experimental design principles can be problematic in some educational settings. Teacher candidates are sorted into teacher preparation programs in nonrandom ways, just as beginning teachers are nonrandomly sorted into schools and groups of students: consequently, it is difficult to control for all the important factors that are likely to influence student outcomes.

Improving learning outcomes for children is a complex process. Both common sense and sophisticated research (e.g., Sanders and Rivers, 1996; Aaronson, Barrow, and Sander, 2003; Rockoff, 2004; Rivkin, Hanushek, and Kain, 2005; Kane, Rockoff, and Staiger, 2006) indicate that teachers have enormously important effects on children’s learning and that the quality of teaching explains a meaningful proportion of the variation in achievement among children. However, understanding that teachers are important to student outcomes and understanding how and why teachers influence outcomes are very different; our charge required us to think carefully about the evidence of the effects of teacher preparation. Student learning is affected by numerous factors besides teaching, many of which are beyond the control of the educational system. Even the factors that are affected by education policy involve intricate interactions among teachers, administrators, students, and their peers.1

Disentangling the role that teachers play in influencing student outcomes is difficult, and understanding the ways in which teacher education influences student outcomes is much more difficult. The design and the delivery of teacher education are connected to outcomes for K-12 students through a series of choices made by teacher educators and by teacher candidates in their roles as students and, later, as teachers. Identifying the empirical effects of teacher preparation on student outcomes poses many


We note the progress that has been made in exploring causal relationships in education in new work supported by the Department of Education and in work synthesized by the What Works Clearinghouse (see http://ies.ed.gov/ncee/wwc/ [September 2009]).

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