Assessing Impacts
One way to summarize these many details is to think in terms of a pair of experimental treatments. The first treatment is the change in performance measures for all teachers. The new evaluation system expands annual evaluations to every teacher, not just pre-tenure teachers. Further, classroom observations are based on a more comprehensive rubric, and teachers’ value-added scores are formally used in their performance evaluations. The second treatment is the change in performance incentives attached to the new measures: new tenure rules that require teachers to score “above” or “significantly above” expectations in both their fourth and fifth years on the job.
I estimate the impacts of these treatments separately and in combination, based on Tennessee data from 2007–08 to 2014–15. I focus on math and English language arts teachers in years 1 through 7 of their careers with students in grades 4–8, who are tested annually in those subjects. In all, my study includes data for 11,000 teachers and 720,000 students.
In my analysis, only teachers hired in 2009–10 or 2010–11 receive both the evaluation and tenure treatments. For these novice teachers, the tenure incentive treatment begins in year 4 and ends after year 5 if they successfully meet score requirements. By contrast, teachers who are in years 4–7 when the new rules begin never experience the tenure incentive treatment. These early-career teachers are subject to new performance evaluations but are already tenured under the old rules.
I focus on changes in teacher value-added in both of these teacher groups. For the novice teachers who receive both treatments, these first estimates capture the additional growth between their first and second, or second and third, years in the classroom. This analysis captures the anticipation effects of the new tenure incentives, because teacher performance only counts toward tenure awards in years 4 and 5 of their career. I then estimate changes in value-added between year 5 and 6, after incentives end, to identify persistent effects of performance incentives. These estimates show the additional growth in value-added, caused by the reforms, on top of the typical growth new teachers experience in their early years on the job.
For the tenured early-career teachers who only receive the evaluation treatment, the estimates describe growth between years 4 and 5, or 5 and 6, or 6 and 7—years when many teachers have completed their most dramatic growth but are continuing to improve. Still, again, these estimates capture the additional growth in value-added net of the average growth observed for teachers in years before the tenure reforms in 2012.
Novice teacher value-added improves by 4.7 percent of a standard deviation in the first year of Tennessee’s reforms (see Figure 2). That gain is in addition to the typical performance growth at the outset of a new teacher’s career. While both math teachers and English language arts teachers experience gains in performance, value-added for math teachers grows by more than twice as much: 6.5 percent of a standard deviation, compared to 2.8 percent of a standard deviation for English language arts teachers.
How much of the improvement in value-added would have occurred without future incentives? Robust new evaluations and feedback can reduce the costs of a teacher’s investment in her skills, but future incentives, like tenure, may increase the returns on a teacher’s investment in her skills. Those future returns alone could generate skill investments and performance gains.
Indeed, I find that value-added for tenured early-career teachers, who do not anticipate or experience the incentive, improves about half as rapidly, by 2.4 percent of a standard deviation. Math teachers improve by 3.6 percent of a standard deviation, while English language arts teacher performance grows by 1.3 percent of a standard deviation.
And what happens when novice teachers’ performance evaluations begin to count toward tenure, starting in year 4? Given that new incentive, we might expect a meaningful improvement in performance; however, I find only a small, estimated increase of 1.3 percent of a standard deviation in teacher value-added between years 3 and 4. This impact is relatively imprecisely estimated, and thus I cannot reject the possibility of no change in their value-added. In other words, the gains to performance overwhelmingly accrue in a teacher’s earliest years when they anticipate the future tenure incentives, but when their performance scores do not yet count for earning tenure.
Nearly two-thirds of novice teachers earn tenure after year 5 of employment, and their scores in year 6 no longer count for tenure. The conventional view of performance incentives would predict a decline in value-added after year 5 when tenure incentives end—but that doesn’t happen. I find suggestive evidence that teachers continue to improve and can rule out any notable decline in performance after the incentive is removed. The persistence of higher value-added is consistent with teachers having improved their skills in response to the new evaluation program’s tenure incentives.
What about the teachers who did not earn tenure? Roughly one-third of teachers do not earn consecutive “above expectations” scores by the end of year 5. These teachers are allowed to continue working in year 6 and beyond under a probationary contract and can eventually earn tenure if they score above the cutoff any two years in a row.