At the extremes, these effects are even more pronounced. Take a group of fifty teachers. The students of the most effective teacher in that group will learn in six months what the students of the average teachers will learn in a year. And those students of the least effective teacher in that group of fifty teachers are likely to take two years to learn the same material. In other words, the very best teachers generate learning in their students at four times the rate of the least effective teachers.
Just as important, teacher quality appears to play a significant role in promoting equality of outcomes. In the United States, many policymakers seem to have assumed that excellence and equity are somehow in tension—that we can have one or the other, but not both. However, evidence from international comparisons has shown that the countries with the high average scores also tend to have a narrow range of achievement (Bursten, 1992; Mullis, Martin, & Foy, 2008; OECD, 2016).
As noted previously, Sanders and Rivers (1996) find that increases in teacher quality confer greater benefits on low achievers than high achievers, and a particularly well-designed study of fifteen- and sixteen-year-olds (Slater, Davies, & Burgess, 2008) also finds that the benefits of having a high-performing teacher are greatest for low achievers (although, interestingly, it also finds that high achievers benefit more than those of average achievement). In their work in kindergarten and first-grade classrooms, Bridget Hamre and Robert Pianta (2005) find that in the classrooms where students make the most progress in reading and mathematics (as measured by scores on the revised Woodcock–Johnson Psychoeducational Battery, a standardized test of cognitive ability and academic achievement), students from socioeconomically disadvantaged backgrounds make as much progress as those from wealthy homes, and those with behavioral difficulties (such as aggressive or defiant behaviors) progress as well as those without. In other words, when teachers are more effective on average, they are disproportionately more effective for at-risk students.
This last finding is particularly important because it shows that Basil Bernstein was wrong—education can compensate for society, provided it is of high quality. Ideally, in the short term, we would concentrate on how to get the highest-quality teachers to the students who need them most—schools will only secure equitable outcomes by ensuring that the lowest-achieving students get the best teachers. In the short term, this means taking the best teachers away from the high-achieving students, which is politically challenging, to say the least.
In the longer term, a focus on improving teacher quality will mean that teacher allocation will no longer be a zero-sum game. Our focus on the achievement gap draws attention to the gap between the high achievers and the low achievers. The problem with thinking about this as an issue of gaps is that one can reduce the gap either by improving the performance of the lowest achievers or by reducing the achievement of the highest achievers. This leads back to the traditional, and now discredited, thinking that equity is the enemy of excellence. Rather than thinking about narrowing the gap, we should set a goal of proficiency for all, excellence for many, with all student groups fairly represented in the excellent. And the way to achieve this is simply to increase teacher quality. As Michael Barber says, “The quality of an education system cannot exceed the quality of its teachers” (Barber & Mourshed, 2007, p. 19).
Ways to Increase Teacher Quality
The realization that teacher quality is the single most important variable in an education system has led to an exploration of how teacher quality can be improved, and there are only two options. The first is to attempt to replace existing teachers with better ones, which includes both deselecting serving teachers and improving the quality of entrants to the profession. The second is to improve the quality of teachers already in the profession.
Because past attempts to improve the performance of serving teachers have achieved so little success, some authors suggest that the only way to improve the profession is through replacement, including both rigorous deselection and increasing the threshold for entry into the profession (see, for example, Hanushek, 2010).
Teacher deselection may be politically attractive—after all, who could possibly be against getting rid of ineffective teachers? But it is hard to do, it may not work anyway, and even when it does work, it is a slow process (see, for example, Winters & Cowen, 2013). First, it is hard to do because, although we know that teachers make a difference, it is very difficult, if not impossible, to work out who really are the least effective teachers. Second, it may not work because, to be effective, you must be able to replace the teachers you deselect with better ones, and that depends on whether there are better potential teachers not currently teaching. Jack Welch famously believes in getting rid of the lowest-performing 10 percent of employees each year (Welch & Welch, 2005). Such an approach sounds a little like the joke that “firings will continue until morale improves,” but even if it does not have a negative impact on those who remain employed, it is only effective if one can replace the deselected 10 percent with better employees. When those recruited to fill the vacancies are worse than those fired, the 10 percent rule is guaranteed to lower average employee quality.
The third problem with deselection is that it is very slow. Replacing the lowest 10 percent with teachers who are only slightly better will take many years to have any noticeable impact on average teacher quality. Given the difficulty with deselecting the right teachers, it is natural that much attention has focused instead on improving the quality of entrants into the profession.
When looking for ways to improve educational achievement, many people look at high-performing countries like Finland and Singapore and note that these countries hold teaching in high regard (Tucker, 2011). Therefore, not surprisingly, many people want to be teachers, so competition for places on preservice teacher preparation programs is intense. For example, at the end of twelfth grade, students at Finnish high schools take a series of end-of-course tests. In addition, all students who want to go on to university in Finland must take a national written test. Those who perform well then take a second test set by the university to which they have applied. In 2014, the University of Helsinki had 1,650 applicants for the 120 places on its preservice teacher program (Sahlberg, 2015). The university selected approximately seventy students based on a combination of their school end-of-course test scores and their scores on the university tests, and fifty students based on the university tests alone. While it is not true to say that Finland recruits only the highest-achieving students, it certainly draws from the highest-achieving one-third of students (Ingersoll, 2007).
In contrast, the United States tends to draw teachers from the lower end of the college achievement range. According to Marigee Bacolod (2007), only around 10 percent of teachers who began their careers in the mid-1980s were academic high achievers in high school (in the top 20 percent), while for other professions, the figure is over 60 percent. This has, predictably, led to calls to recruit more academic high achievers into teaching. The problem with this attractive solution is that there is little evidence that academic achievement has much of a relationship with teacher quality (Harris & Sass, 2009).
Now this does not, of course, mean that academic ability is unimportant in teaching—clearly a certain amount of academic ability is necessary to be a teacher—and so it probably makes sense to require teachers to have college degrees. But what many people find surprising is that, beyond this, qualifications do not seem to matter much (Harris & Sass, 2009). Teachers with higher college grade point averages do not seem to be any more effective than other teachers. Perhaps even more surprisingly, teachers with master’s degrees in education are no more effective than those with just a bachelor’s degree (Harris & Sass, 2009). Some researchers have gone so far as to claim that the only teacher variable that consistently predicts how much students will learn is teacher IQ (Hanushek & Rivkin, 2006), although other studies (like Harris & Sass, 2009) find no consistent relationship between teachers’ intellectual abilities and the progress of their students.