The willingness of policy makers and taxpayers to devote such a large proportion of education dollars to teachers highlights the undisputed importance of teachers in realizing educational goals. A number of researchers have argued that teacher quality is a powerful predictor of student performance. In her analysis of teacher preparation and student achievement across states, Darling-Hammond (2000) reports that “measures of teacher preparation and certification are by far the strongest correlates of student achievement in reading and mathematics, both before and after controlling for student poverty and language status.” She contends that measures of teacher quality are more strongly related to student achievement than other kinds of educational investments such as reduced class size, overall spending on education, and teacher salaries. 2
It is not surprising that the academic caliber of teachers varies a good deal by subject area, given that STEM majors tend to have higher SAT scores than non-STEM majors. For all three cohorts, STEM majors’ SAT score average is about 100 points higher in each year than that of non-STEM majors, and a far higher proportion come from the top 20 percent of the distribution. For both the 1993 and 2000 cohorts, teachers score lower on average than nonteachers among both STEM majors and non-STEM majors, in some cases by as much as 7 SAT percentile rank points (see Figure 2). However, in the case of the 2008 cohort, scores for teachers were slightly higher for both STEM majors (by about 3 percentile rank points) and non-STEM majors (by about 2 percentile rank points) than for nonteachers. In other words, we find that high-scoring STEM majors are relatively more likely to become teachers in 2008 than they were in earlier cohorts. There is still considerable overlap in the distributions of scores for teachers and nonteachers in both groups, but the gap in the academic proficiency of teachers and graduates entering other professions had clearly narrowed a great deal—and even reversed—by 2008. Particularly notable is the fact that there has been a sharp decline in the share of STEM majors entering teaching from the bottom 20 percent of the SAT distribution, which fell from 13 percent in 1993 to less than 2 percent in 2008.