How to Improve the Supply of High-Quality Teachers

Virtually everybody interested in improving the performance of schools concentrates on the importance of teacher quality. Yet policy recommendations related to teacher quality frequently do not incorporate existing evidence about performance. This paper reviews the various strands of research related to teacher quality including: the role of aggregate salaries, the supply of teachers with different characteristics, the relationship between teacher characteristics and student achievement, and direct estimates of the value-added of teachers. This evidence is then related to current policy initiatives as generally bounded by recommendations to tighten up on teacher qualifications and recommendations to loosen up on entry with stronger subsequent incentives. ∗ Stanford University, National Bureau of Economic Research, and University of Texas at Dallas; Amherst College, National Bureau of Economic Research, and University of Texas at Dallas, respectively. This research has been supported by a grant from the Packard Humanities Institute. How to Improve the Supply of High Quality Teachers By Eric A. Hanushek and Steven G. Rivkin When considering schools, one cannot help but pay attention to teachers. After all, teachers are the largest single budget item of schools, and, more importantly, many believe that they are the most important determinant of school quality. Yet research does not find a systematic link between teacher characteristics and student outcomes, leading to doubts about many current policy thrusts that are keyed to measurable attributes of teachers and their background. The relevant research follows four distinct lines that relate in varying ways to teacher quality. At the most aggregate level and possibly the most influential, a variety of studies have traced changes over time in the salaries of teachers relative to those in other occupations. Going beyond that, a second level of studies relates pay and other characteristics of teaching jobs to the characteristics of teachers in different schools and districts and teacher turnover. A third line of research, following naturally from these, relates teacher characteristics to student performance. It is the failure to find a strong relationship between the contributions of teachers to student achievement and other outcomes on the one hand and teacher education, experience and salaries on the other that is so inconsistent with the popular view of teachers as a key determinant of the quality of education. Finally, the fourth line of research appears to have solved this conundrum by demonstrating both the large impact of teachers on student learning and the lack of explanatory power of traditional quality measures. The central focus of this paper is to relate these various bodies of research to a set of teacher quality policy initiatives. These proposals can be divided into three broad areas that are not mutually exclusive. First, because salaries of teachers have fallen relative to other jobs, some argue an obvious move is simply to restore teacher salaries to their previous position in the earnings distribution in order to attract better teachers into the profession. Second, states should adopt more stringent qualifications for teachers such as mandatory Master’s Degrees in order to improve quality. Salary increases are often but by no means always recommended along with more stringent qualifications in order to offset any possible negative impacts on teacher supply. Finally, an alternative set of policy proposals has taken a very different tact. These typically advocate less strict rather than stricter requirements in combination with incentives for higher teacher performance and improved school personnel practices. We begin with a discussion of the existing research on teachers. This provides the backdrop for a more thorough discussion of the policy options. Research on Teacher Quality While the evidence related to teacher quality is widely scattered, there are common themes. A key distinction is whether or not the investigations are related directly to student outcomes or simply rely upon a presumed relationship. Aggregate Salary Trends A starting point in the consideration of teacher quality is the evolution of teacher salaries over time. Figure 1 traces the wages of teachers aged 20-29 compared to those of other young college graduates between 1940 and 1990. The calculations, done separately by gender, give the proportion of nonteachers with a bachelor’s degree or more who earn less than the average teacher. Over the entire time period since WWII, salaries of young female and male teachers have fallen relative to those for other occupations. However, there are substantial gender differences in the time path of relative salaries. For males, relative salaries fell between 1940 and 1960 but have remained roughly constant afterwards. For females, relative salaries started out high – above the median for college educated females – but then continuously fell. The changes are easiest to see for young teachers and college graduates, where the adjustment has been larger, but they also hold for teachers of all ages (see Hanushek and Rivkin (1997)). In other words, the growth in late career salaries has not offset the decline in salaries for younger teachers. Others have attempted to go deeper into the structure of teacher supply responses. Flyer and Rosen (1997) describe a more formal model of changing female opportunities and its impact on the teaching profession. Lakdawalla (2001, 2002) extends this to concentrate on the role of productivity changes in competing industries. There can be little doubt that technological change, expanded opportunities for women, growth in international trade and other factors that have increased the demand for highly skilled workers have placed upward pressure on teacher salaries. The decline in the relative earnings of teachers has likely led to a fall in average teacher quality over this period, though the shorter term implications of a change in relative earnings is less clear cut (Ballou and Podgursky (1997)). However, the extent of that quality decline is unclear and depends in large part on the correlation between teaching skill and the skills rewarded in the non-teacher labor market. In a simple unidimensional skill framework in which non-pecuniary factors play no role, the substantial decline in relative salary would be expected to lead to a large fall in teacher quality. However, a more complex and realistic framework in which the skill set of teachers differs from that of other professionals suggests the possibility of a more muted response to the salary changes. For example, if teaching places greater emphasis on a set of communication and interpersonal relation skills than the general labor market, the salaries relative to all college graduates may not provide a particularly good index of teacher quality. 1 Note that salaries for teachers include all earnings, regardless of source. Thus, any summer or school year earnings outside of teaching are included. No adjustments are made, however, for any differences in the length of the school day or in the days worked during the year. Nor is any calculation of employer paid fringe benefits made. A clear discussion of the importance of each of these along with interpretation of the overall salary differences can be found in (Podgursky (2003). For the time series comparisons, these omitted elements of compensation are most relevant, if there have been relative changes in the importance of them between teachers and nonteachers over time. We currently have little data on any such changes. Figure 1. Percent college educated earning less than average teacher, by gender, age 20-29 from 1940-2000