Random Assignment and Analytical Strategy

Within each school, students in the same grade were randomly assigned to either an AC teacher or a TC teacher. Each instance in which we conducted random assignment constituted a "mini-experiment"—achievement of students in a classroom taught by an AC teacher was compared to achievement of students in a classroom taught by a TC teacher. Because students in the classrooms were randomly assigned within the same school, the characteristics and motivations of students for each teacher pair⁶ did not systematically differ, and the contextual situation was the same. This was done to minimize preexisting differences in students and schools that might influence teacher practices and student test scores. Thus the difference in student test scores can be attributed to the type of teacher and not student, classroom, or school characteristics. T-tests confirmed that there were no statistically significant differences in demographic characteristics, including gender, race/ethnicity, and eligibility for free or reduced-price lunch, or baseline achievement levels between students assigned to AC or TC teachers. In addition, the integrity of random assignment was well maintained: fewer than 3 percent of students originally assigned to one type of classroom switched over to the other type.

An important distinction of this design is that because certification routes are not randomly assigned to teacher trainees, the estimates of the effects on student achievement and classroom practices of teachers who were trained through different routes to certification pertain to those who chose to participate in these programs. Because of likely differences in the types of people who attend various certification programs, the results cannot be used to rigorously address how a graduate of one type of program would fare if he or she had attended another type. The study design and the collection of extensive data on teacher characteristics and experiences facilitate answering the second research question, concerning how student achievement and teacher practices are associated with teachers' training experiences toward initial certification. These findings are suggestive, however, because teachers were not randomly assigned to training programs or to their personal characteristics.

To estimate the effects of teachers who chose to be trained through different routes on student achievement and the classroom practices experienced by students, we compared teachers from AC programs with teachers in the same schools and grades who completed a TC program. We also estimated two subgroups—AC programs with low and high amounts of required coursework—to investigate separately the comparison of (1) AC teachers from low-coursework programs relative to their TC counterparts, and (2) AC teachers from highcoursework programs relative to their TC counterparts.⁷ The comparison between AC and TC teachers overall provided an experimental estimate of the average difference in student achievement of teachers from the two routes, a comparison useful to principals and school administrators because it provides an indication of how students might perform when instructed by an AC teacher compared to a TC teacher. The subgroup estimates are of interest independent of the overall estimate, since there is variation in the amount of coursework required by state or district certification policy. The subgroup analyses allow us to determine, within an experimental framework, the effects on student achievement and classroom practices experienced by students of teachers who attended programs with a relatively large difference in required coursework as demonstrated by the comparison between teachers from low-coursework AC programs and their TC counterparts. We can also examine the effects on students of teachers who attended programs with relatively little difference in required coursework as demonstrated by the comparison between teachers from high-coursework AC programs and their TC counterparts.⁸

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