When researchers ran the numbers in dozens of different studies, every factor under a school’s control produced just a tiny impact, except for one: which teacher the student had been assigned to. Some teachers could regularly lift their students’ test scores above the average for children of the same race, class and ability level. Others’ students left with below-average results year after year. William Sanders, a statistician studying Tennessee teachers with a colleague, found that a student with a weak teacher for three straight years would score, on average, 50 percentile points behind a similar student with a strong teacher for those years. Teachers working in the same building, teaching the same grade, produced very different outcomes. And the gaps were huge. Eric Hanushek, a Stanford economist, found that while the top 5 percent of teachers were able to impart a year and a half’s worth of learning
Consider a bar graph presented at a recent talk on teaching, displaying the number of Americans in different professions. The shortest bar, all the way on the right, represented architects: 180,000. Farther over, slightly higher, came psychologists (185,000) and then lawyers (952,000), followed by engineers (1.3 million) and waiters (1.8 million). On the left side of the graph, the top three: janitors, maids and household cleaners (3.3 million); secretaries (3.6 million); and, finally, teachers (3.7 million). Moreover, a coming swell of baby-boomer retirements is expected to force school systems to hire up to a million new teachers between now and 2014.o students in one school year, as judged by standardized tests, the weakest 5 percent advanced their students only half a year of material each year.