Mystery of good teaching: the evidence shows that good teachers make a clear difference in student achievement. The problem is that we don't really know what makes a good teacher

Education Next, Spring, 2002 by Dan Goldhaber

WHO SHOULD BE RECRUITED TO fill the two to three million K--12 teaching positions projected to come open during the next decade? What kinds of knowledge and training should these new recruits have? These are the questions confronting policymakers as a generation of teachers retires at the same time that the so-called baby boom echo is making its way through the education system. Key to answering these questions is knowing how much influence teachers have over student achievement and what specific teacher attributes lead to higher student achievement, For instance, does holding a master's degree make one a better teacher? Do the best teachers hail from elite universities? Did they earn high GPAs in college? Did they major in the subject they are teaching? How much does experience matter? Do traditional, university-based teacher-preparation programs produce the best teachers, or are alternatively certified teachers just as good?

These questions are particularly relevant given that researchers have raised concerns about the overall quality of today's teaching workforce. As measured by standardized test scores (mainly the SAT and the ACT), students choosing to major in education tend to be drawn from the lower end of the ability distribution, In Who Will Teach?, Harvard University professor of education Richard Murnane and his colleagues write: "College graduates with high test scores are less likely to take [teaching] jobs, employed teachers with high test scores are less likely to stay, and former teachers with high test scores are less likely to return." On average, according to the findings of University of Massachusetts economist Dale Ballou, the higher the quality of an individual's undergraduate institution, the less likely a student is to choose a teaching career, Moreover, during the past 25 years the share of master's and doctoral degrees in education granted by toptier public and private research universities has declined dr amatically. And of students who graduated from college in 1993 and 1994, data from the Baccalaureate and Beyond survey show that those who entered the public school teaching profession averaged a 923 on the SATs; the average SAT of those entering other professions was about 80 points higher. The results are even more dramatic when one compares the SATs of teachers with those of people entering technical professions, such as engineering.

The demographic shifts of the next decade provide the opportunity to thoroughly remake the teaching profession. This is a significant opportunity, given that the evidence suggests that teacher quality is the most important school factor in explaining differences in student performance. The difficulty from a policy perspective is that the relationship between readily quantifiable attributes--such as a teacher's highest degree attained or level of experience--and student outcomes is tenuous at best, In other words, good teachers certainly make a difference, but it's unclear what makes for a good teacher,

Overall Impact

Research dating back to the 1966 release of Equality of Educational Opportunity (the "Coleman Report") shows that student performance is only weakly related to school quality. The report concluded that students' socioeconomic background was a far more influential factor, However, among the various influences that schools and policymakers can control, teacher quality was found to account for a larger portion of the variation in student test scores than all other characteristics of a school, excluding the composition of the student body (so-called peer effects).

Much of the research published since the Coleman Report has confirmed the finding that high-quality teachers raise student performance--indeed, it appears that the most important thing a school can do is to provide its students with good teachers. The Coleman Report's finding was based on the influence of a set of quantifiable teacher characteristics, such as years of experience, education levels, and performance on a vocabulary test, Since then, due in large part to the availability of new data sources that link and track teachers and students over a number of years, researchers have been able to estimate the overall contribution of teachers to student learning. This includes not only the effect of easily measurable attributes, such as experience and degrees obtained, but also the effect of harder to measure intangible attributes, such as a teacher's enthusiasm and skill in conveying knowledge.

Tennessee is one of the few states with data systems in place that track teachers over time and link them to their students' achievement scores. Researchers who have studied the Tennessee data, mainly former University of Tennessee professor William Sanders and his colleagues, found that the effectiveness of teachers has more of an influence on student achievement than any other schooling factor, They also found a wide range of effectiveness among teachers; there are some very good teachers, some very bad teachers, and a wide range of performance between them. Using the "Sanders methodology;' teachers are placed into effectiveness quintiles based on their students' growth in achievement, or the "value added" by the teachers. Those teachers who fall into the first quintile, the least effective teachers, were found to elicit average student gains of roughly 14 percentile points a year. The most effective teachers elicited an average gain of 52 percentile points a year. The effects of teacher quality were also found to persist for years after a student had a particular teacher.