Given that teachers are important, the important research task is to identify the characteristics that distinguish quality teachers and to determine how those characteristics can be enhanced. Let's go through the characteristics assumed to be important in ESEA and take a look at the related research.
Certification and licensure
The issue of certification has generated more heat than light. You would think it would be simple to compare student achievement for certified versus uncertified teachers, but it is not. One reason is that states typically require some form of certification or licensure for a teacher in the public schools within some period of time after the teacher begins employment. Thus teachers without certification are typically inexperienced beginners. That means that simple comparisons of certified versus uncertified teachers are biased by differences in experience and age. Second, the issue of certification is often confused with the issue of alternative certification, which is a route to a teaching license that bypasses some of the undergraduate coursework requirements in education. Sometimes arguments for or against alternative certification are made on the basis of comparisons of teachers with certificates, including alternative certificates, with teachers working with provisional or temporary licenses. Third, the issue of certification is often confused with the issue of out-of-field teaching. Generally, out-of-field teachers, e.g., someone with a degree in English who is teaching math, are certified. Arguments for or against certification based on comparing out-of-field and in-field teaching are thus inappropriate. Fourth, the definitions and requirements for licensure and certification differ substantially from state to state, and sometimes within jurisdictions within the same state. These differences make it difficult to know exactly what is being compared when data are aggregated across states and jurisdictions.
With those caveats in mind, my reading of the research is that the evidence for the value of certification in general is equivocal at best. For example, Goldhaber and Brewer (1998) analyzed data from over 18,000 10th graders who participated in the National Education Longitudinal Study of 1988. After adjusting for students' achievement scores in 8th grade, teacher certification in 10th grade was not significantly related to test scores in 10th grade. In another study, notable because it uses experimental logic rather than the correlational approaches that dominate study of this topic, Miller, McKenna, and McKenna (1998) matched 41 alternatively trained teachers with 41 traditionally trained teachers in the same school. There were no significant differences in student achievement across the classrooms of the two groups of teachers.
A study by Darling-Hammond (1999) stands in contrast to the many studies that find no effects or very small effects for teacher certification. She related scores on the National Assessment of Educational Progress at the state level to the percentage of well qualified teachers in each state. "Well qualified" was defined as a teacher who was fully certified and held the equivalent of a major in the field being taught. For generalist elementary teachers, the major had to be in elementary education; for elementary specialists, the major had to be in content areas such as reading, mathematics, or special education. Darling-Hammond reported that teacher qualifications accounted for approximately 40 to 60 percent of the variance across states in average student achievement levels on the NAEP 4th and 8th grade reading and mathematics assessment, after taking into account student poverty and language background.
Although this study is frequently cited, the approach of aggregating data at the level of the state is seriously problematic. It goes backwards in terms of aggregation from the work of Coleman whose findings are considered suspect because the analyses were of data at the school level. Students do not experience a teacher with the average level of certification in a state; they experience a teacher who is or is not certified. The aggregation bias may account for Darling-Hammond's estimates of the effects of certification being light years out of the range of effects that have been reported by all other studies of this topic.
Subject matter knowledge
The effects of teacher training on academic achievement become clearer when the focus becomes subject matter knowledge as opposed to certification per se. The research is generally consistent in indicating that high school math and science teachers with a major in their field of instruction have higher achieving students than teachers who are teaching out-of-field (e.g., Brewer & Goldhaber, 2000; Monk, 1994; Monk & King, 1994; Rowan, Chiang, & Miller, 1997). These effects become stronger in advanced math and science courses in which the teacher's content knowledge is presumably more critical (Monk, 1994; Chiang, 1996).
The best studies, including the ones cited here, control for students' prior achievement and socio-economic status. Studies that simply report the association between teachers' undergraduate majors and student achievement are difficult to interpret. For instance the year 2000 National Assessment of Educational Progress in math reports that eighth-graders whose teachers majored in mathematics or mathematics education scored higher, on average, than 8th graders whose teachers did not major in these fields. However, there are many interpretations of this simple association, including a well-documented rich-get-richer process in which students with higher math abilities are assigned to classes taught by better trained teachers.
Interestingly, the 2000 NAEP finds no relationship between math scores at 4th grade and teachers' major. Likewise, Rowan (2002) using a different dataset found no relationship in elementary school between certification in math and student achievement in math, and no relationship between having a degree in English and student achievement in reading. These findings suggest that subject matter knowledge in these areas as currently transmitted to teachers-in-training by colleges of education is not useful in the elementary school classroom.
General knowledge and ability
The most robust finding in the research literature is the effect of teacher verbal and cognitive ability on student achievement. Every study that has included a valid measure of teacher verbal or cognitive ability has found that it accounts for more variance in student achievement than any other measured characteristic of teachers (e.g., Greenwald, Hedges, & Lane, 1996; Ferguson & Ladd, 1996; Kain & Singleton, 1996; Ehrenberg & Brewer, 1994).
This is troubling when joined with the finding that college students majoring in education have lower SAT and ACT scores than students majoring in the arts and sciences. For example, among college graduates who majored in education, 14% had SAT or ACT scores in the top quartile, compared to 26% who majored in the social sciences, compared to 37% who majored mathematics/computer science/natural science. In addition, those who did not prepare to teach but became teachers were much more likely to have scored in the top quartile (35 percent) than those who prepared to teach and became teachers (14 percent) (NCES, 2001).
In general, studies of the effects of teacher experience on student achievement suggest a positive effect. For instance, Rowan (2002) found a significant effect of teaching experience on reading and math outcomes in elementary school, with larger effects for later elementary school than early elementary school. Likewise, Greenwald, Hedges, and Laine (1996), in their large meta-analysis of the literature on school resources and student achievement, found significant effects of teacher experience.
Many districts and states provide incentives for teachers to return to the classroom to obtain advanced degrees in education. The bulk of evidence on this policy is that there are no differential gains across classes taught by teachers with a Masters' degree or other advanced degree in education compared to classes taught by teachers who lack such degrees.
Intensive and focused in-service training
Although the literature on professional development is voluminous, there are only a few high quality studies relating teacher professional development experiences to student outcomes. Recommendations for "high quality" professional development tend to emphasize the importance of more intense, content-focused experiences (i.e., not one-day generic workshops), as well as more opportunities for peer collaboration and more structured induction experiences for new teachers. These recommendations are reasonable, but are supported by little more than anecdotal evidence, inferences based on theories of learning, and survey data indicating that teachers feel they get more from such experiences than from typical workshops.
One relatively strong study supporting the value of focused professional development is by Cohen and Hill (2000). These investigators compared the effects of teacher participation in professional development specifically targeted to a mathematics education reform initiative in California compared to teacher participation in special topics and issues workshops that were not linked to the content of the mathematics initiative (e.g., workshops in techniques for cooperative learning). The more time teachers spent in targeted training on the framework and curriculum of the mathematics reform, the more their classroom practice changed in ways that were consistent with the mathematics reform, and the more they learned about the content and standards for that reform. Teachers who participated in special topics and issues workshops showed no change in their classroom practice or knowledge related to the reform. Teachers who participated in the focused training and whose classroom practice moved towards incorporating the framework of the new math initiative had students who scored higher on a test of the math concepts imparted by the new curriculum.
This study and a couple of others (Wiley and Yoon, 1995; Brown, Smith, and Stein, 1996; and Kennedy, 1998) suggest that when professional development is focused on academic content and curriculum that is aligned with standards-based reform, teaching practice and student achievement are likely to improve.
Summary of the effects of teacher characteristics on student achievement
The figure that follows attempts to summarize the relative strength of each of the dimensions of teacher quality I have reviewed. The heights of the bars in the graph should not be taken as exact or specific to any particular research study. Rather they are intended simply to summarize graphically the conclusions I have drawn in the preceding narrative.