Abstract
Most studies that have fueled alarm over the attrition and mobility rates of teachers have relied on proxy indicators of teacher quality, even though these proxies correlate only weakly with student performance. This paper examines the attrition and mobility of early-career teachers of varying quality using value-added measures of teacher performance. Unlike previous studies, this paper focuses on the variation in these effects across the effectiveness distribution. On average, more effective teachers tend to stay in their initial schools and in teaching. But the lowest performing teachers, who are generally the most likely to transfer between schools, appear to "churn" within the system, and teacher mobility appears significantly affected by student demographics and achievement levels.
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Introduction
The evidence that teacher quality is the key schooling factor influencing student outcomes
(Aaronson, Barrow, and Sander 2007; Goldhaber, Brewer, and Anderson 1999; Rivkin,
Hanushek, and Kain 2005; Rockoff 2004) raises significant concerns over teacher attrition and
sorting in public schools. In particular, research generally shows that the most academically
prepared teachers—measured by ACT scores, college selectivity, and degrees in technical
subjects—are most likely to leave teaching, and the most qualified teachers—measured by such
attributes as licensure status, the selectivity of the colleges from which they graduated, and their
performance on standardized exams—are most likely to leave high-poverty and minority schools
(Hanushek, Kain, and Rivkin 2004; Lankford, Loeb, and Wyckoff 2002).
When these patterns of sorting and attrition are coupled with evidence of a correlation
between teachers' academic proficiency and student achievement (Clotfelter, Ladd, and Vigdor
2007; Ehrenberg and Brewer 1994, 1995; Ferguson 1991; Ferguson and Ladd 1996; Goldhaber
2007; Strauss and Sawyer 1986; Summers and Wolfe 1975), it is tempting to conclude that
public schools are losing many of their most effective teachers and keeping too many of their
least effective teachers. This conclusion, however, would be premature since a great deal of
evidence suggests that easily observed and quantifiable teacher attributes (credentials, test
scores, and so on) are only weakly correlated with student standardized assessment performance
(Aaronson et al. 2007; Clotfelter et al. 2007; Goldhaber and Brewer 2001; Gordon, Kane, and
Staiger 2006; Greenwald, Hedges, and Laine 1996). Moreover, recent studies that measure
teacher quality based on test score gains made by a teacher's students have found that, on
average, more effective teachers tend to stay in the classroom (Hanushek et al. 2005; Krieg 2006;
West and Chingos 2008). Average trends, however, can mask important variation in behavior
across teachers with different levels of effectiveness. Thus, it is worth examining differences in
mobility behavior and asking: "Are public schools keeping their 'best' teachers, and what
conditions predict who stays and who goes?"
We investigate these questions by studying the career paths of new elementary teachers
who began teaching in North Carolina in 1996?2002. Our six-year panel allows us to explore the
earlier career paths of teachers including transfers from one teaching position to another within
and between school districts, and exits from the North Carolina public school workforce. And,
because teachers can be matched to the students in their classrooms, we explore how career
transitions relate to a more direct measure of worker quality: estimates of teachers' value-added
contributions toward student learning.
Our review of the literature finds only four papers that examine teacher mobility and its
relationship with effectiveness (we use the terms "effectiveness," "quality," "productivity," and
"job performance" interchangeably); all four find, contrary to expectations, that more effective
teachers were less likely to leave their schools, and most find that more effective teachers were
less likely to leave the profession. Krieg (2006) (the only study currently published by a peerreviewed
journal) uses a single year of fourth-grade test scores merged with a panel of teacher
observations from Washington State to investigate the decision to leave the profession. He finds
that, on average, more effective female teachers (measured by value-added models) are less
likely than less effective females to leave the profession the following year. The effect is
negligible for males.
Hanushek and colleagues (2005) examine teacher exit and transfer behavior in a large
urban district in Texas and find that teachers who change campuses within a district, change
districts, or leave public education in Texas entirely are, on average, less effective than those
teachers who stay at the same campus. Interestingly, evidence suggests that exiting teachers are
of lower quality only in the year immediately preceding their departure. Similarly, Boyd and
colleagues (2007) find in their analysis of teachers in New York City that more effective teachers
tend to stay in the classroom.
West and Chingos (2008), in a descriptive analysis, reach a somewhat different
conclusion than the authors described above. These authors find that the best performing teachers
are more likely to stay in their initial schools than less effective teachers.1 However, the Florida
state school system appears to lose its highest performing teachers at approximately the same
rate as their lowest performing teachers, with 40 percent of the highest performing teachers
leaving the system within five years.
These studies suggest a modicum of good news to those concerned with teacher mobility
and attrition: public schools are, on average, not "losing their best teachers." These studies,
however, do not provide all the relevant detail we need to understand the relationship between
teacher effectiveness and mobility. For example, only West and Chingos (2008) directly examine
the propensity to leave schools at different points along the distribution of teacher effectiveness.
This is important if we are concerned, for instance, with whether school systems are retaining
their very best teachers and/or encouraging their least effective teachers to find an alternative
occupation—a question of great policy interest (see Gordon et al. 2006 and Hanushek
forthcoming). In addition, these studies do not fully conceptualize the factors that play a role in
teacher attrition. While they each focus on the organizational factors (e.g., student population
and school size), they do not directly consider important local labor market considerations such
as the marketability of teachers and conditions in the local teacher and external labor markets. As
we go on to describe in the next section, it is only through assessing all these issues that it is
possible to fully understand the ramifications of teacher mobility for schools serving different
types of students and the school system as a whole.
In the end we find, as others have, that the system's most effective teachers are, on
average, more likely to stay in teaching, to stay in their current district, and even to stay in their
current school than less effective teachers. But a deeper look at the issue shows that the factors
predicting teachers' moves vary across the effectiveness distribution in ways that are not ideal
for minimizing the loss of the system's best teachers, especially from schools serving the most
challenged populations, or for minimizing the churn of its least effective teachers. Specifically,
our findings reinforce concerns some have expressed about how often the lowest performing
teachers are identified and removed from classrooms as opposed to just shuffled throughout the
education system (a phenomenon commonly referred to as "the dance of the lemons").2 They
also reinforce concerns that many highly effective teachers leave disadvantaged schools and that
those who have good opportunities outside the teacher labor market are enticed to leave the
profession.3
In the next section we provide a conceptual discussion of teacher mobility and the
relationship between teacher effectiveness and mobility.
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