Teacher unions have long argued that the main criteria to be used in determining whether teachers are effective or not should be variables like teaching experience and teaching credentials rather than subjective evaluations of principals and other administrators. The unions claim that these evaluations were likely to be biased because allegedly they would be greatly affected by whether administrators liked or disliked particular teachers instead of by their actual classroom performance.
Unions and their supporters have also argued that teacher evaluations by administrators or parents are not worth a lot because it is difficult to get agreement on who are the good and bad teachers. I would challenge that claim: most of the time students as well as teachers agree on who are the good and bad teachers. Even my grandchildren in the lower grades of elementary school are confident that they and other students know which teachers to avoid, and which to try to get. Nevertheless, to provide more objective measures, teacher evaluations have been shifting toward using performance on standardized tests that measure knowledge of math, science and English language-related subjects. Teachers whose students perform well on these tests are deemed good teachers, whereas those with poorly performing students are considered weak teachers.
Teacher unions all over the country have fought against using performance-based measures to evaluate teachers, but the unions are gradually losing this battle. More than half of all U.S. states have adopted policies that require teachers to be rated in part based on student performance, such as standardized test scores. Even in their “victory” in the Chicago strike, the teachers union could not eliminate the use of student performance measures in evaluating teachers, but succeeded only in getting its weight in teacher evaluations down to 25% in the first two years of the contract, 30% in the third year, and 40% in year 4-the city wanted a weight of 40% starting in teh first year of the contract.
Of course, actual test scores are not appropriate measures of teacher contribution since some teachers get students who are better prepared when they enter their classes. For this reason the criterion used in evaluating teachers by many school systems and also by academic articles on school reform is the value added (VA) by teachers to student performance; namely, the improvements in students’ test scores as a result of taking classes of different teachers. The New York Times and the Los Angeles Times have in recent years released VA results for some the teachers in the New York and Los Angeles school districts, despite the loud protests of teachers unions in these cities.
Even value added may not fully measure the relevant effects of teachers on student performance since, for example, a given improvement in test scores may be more (or less) important for students with low test scores than for those who had high scores. More importantly, the fundamental way to judge teachers is not how their students do on tests, but how different teachers affect the likelihood that their students finish high school and go to college, how teachers affect the earnings of their students after they enter the labor force, and whether their students get involved in gangs and crimes.
A small number of recent academic studies have tried to see how well VA measures predict how students do when they become adults. A summary of a good study along these lines by Raj Chetty, John Friedman, and Jonah Rockoff was published this summer in the journal Education Next under the title “Great Teaching”. They had access to data for a large urban school district that spanned the 20 years from 1988-89 through 2008-09. The data contained information on test scores for about 2.5 million children in grades 3 through 8, and also the schooling, and when available, earnings of the children after they finished these grades.
They find large effects on subsequent adult earnings when these young students had teachers who produced good improvements in test scores compared to the adult earnings of students who had teachers who produced little improvement in test scores. If teachers were paid in relation to their effects on the subsequent adult earnings of their students, these results imply that teachers with good VA ratings should be paid considerably more than teachers with bad ratings. Adopting such a payment system for teachers would produce an improvement in the quality of teaching because good teachers would be more willing to go into teaching at elementary and high school grades. Such a change may well induce an increase in overall spending on teachers’ salaries and benefits because taxpayers would be willing to support education more generously if they felt students were getting good and useful teaching.
Of course, further studies of the effects of teachers on value added and on variables like adult earnings may find much smaller effects than those found by Chetty, et al. Yet their finding that good teachers make a big difference to student performance is not the least bit surprising. This makes it all the more unfortunate that for decades teachers unions have fought against merit pay for good teachers, no matter how “good” teaching were to be measured. Since parents are losing patience with bad teachers, I expect the issue of merit pay to be one of the coming battlegrounds between teachers unions, and school boards and parents that want to better prepare students for the rigors of the modern marketplace.