Main Effects
All of the research reviewed to this point is correlational in nature and focuses on differences across teachers. The history of this line of research flows from attempts to demonstrate that teachers and classrooms make a difference, to determining how much of a difference they make, to trying to identify characteristics of teachers that contribute to those differences. Within psychology, this is called differential psychology or the study of individual differences.
There is another tradition within psychology that is relevant to attempts to improve teacher quality. That is the experimental tradition. It looks not for individual differences among teachers but for interventions that raise the effectiveness of all teachers. These are called main effects. Unfortunately experimental methods have not yet found their way to research on teacher training. Even so there are data of a weaker nature that suggest experiences and policies that can produce main effects, i.e., can raise the performance of all teachers and through them the achievement of all students. These data demonstrate the effects of the contexts in which teachers work. There are many dimensions to the context of teaching. Here I focus on the components of standards-based educational reform that are embodied in the ESEA reauthorization and the ongoing practice of many states. These components are: 1) learning standards for each academic subject for each grade, 2) assessments that are aligned to those standards, and 3) provisions for holding educators accountable for student learning. For standards-based reform to work there is reason to think that two additional components are necessary: 1) teachers must be provided with curriculum that is aligned with the standards and assessments; and 2) teachers must have professional development to deliver that curriculum.
We can see the effect of curriculum in the next figure. Three schools in Pittsburgh that were weak implementers of a standards-based math curriculum were compared with three schools with similar demographics that were strong implementers. Note that racial differences were eliminated in the strong implementation schools, and that performance soared. There is no reason to believe that any of the individual differences in teachers previously described, such as cognitive ability or education, differed among the weak implementation schools versus the strong implementation schools. Yet the teachers in the strong implementation schools were dramatically more effective than teachers in the weak implementation schools. Thus a main effect of curriculum implementation swamped the effects of individual differences in background among teachers.
We see this effect on a larger scale in a database developed by the American Institutes of Research under contract to the U.S. Department of Education. The database includes academic achievement data and demographic data on each school in 48 different states that have their own assessment system. The Education Trust has analyzed the data to ask the question of how many high-poverty and high-minority schools have high student performance. They have identified 4,577 high-flying schools nationwide that are in the top third of poverty in their state and also in the top third of academic performance. Whatever these schools are doing to perform so well, and we need to understand that better than we do now, it is very unlikely that they have teachers who are dramatically different from teachers in less effective schools on the individual differences previously surveyed. Again, there is a main effect, something going on in the school as a whole that affects the practice of all teachers in the school, and raises student achievement accordingly.
The next table examines main effects at a higher level, in this case for states. Here we see 4th grade math gains on the National Assessment of Educational Progess for African Americans between 1992 and 1996 for the United States as a whole and for three states (Massachusetts, Texas, and Michigan) that beat the national increase by a substantial margin.
United States: + 8
Massachusetts: +14
Texas: + 13
Michigan: + 13
The next figure continues this same theme by demonstrating how North Carolina outpaced the United States as a whole in gains in 4th grade reading between 1992 and 1998.
| United States | North Carolina | |
| Overall | 0 | +5 |
| African American | +1 | +6 |
| Latino | -4 | +4 |
| White | +2 | +6 |
Again, something is going on that generates better performance from all teachers regardless of the individual differences in education and cognitive abilities they bring to the classroom.