Individuals who have entered public school teaching in the 1990s and onward are less qualified for teaching than individuals who entered public school teaching in earlier decades (despite modest improvements in the past decade according to one study). According to a 2008 study based on SAT data, “education majors finished 25th in reading, 27th in math and a combined 57 points below the national average in both.” Teacher decline since the 1960s based on other earlier credible ability measures has been confirmed in multiple studies.
So, my simple theory (which I thought of independently but I am by no means the first person to propose this theory) is that the majority of public school* teachers—particularly at lower levels—have historically been women. The older (now retired or retiring) generation of women who chose to become teachers went in when the profession attracted more intelligent women. The teaching profession was a particularly attractive profession for women. Besides the inherent advantages to teaching (working with children, summers off, etc.), this attractiveness was due to a combination of traditional social norms and employer discrimination against women in other professions that intelligent men would enter. Teaching was one of the more prestigious and socially acceptable jobs for women to enter in the 1960s and 70s.
*The reason I don’t discuss private school teachers is I think there are often different incentives at work for those who go into private school teaching. At religious private schools, teachers may go into teaching due to religious motivation. Or, alumni may be more likely to return to the school to teach than at a public school. I simply don’t know enough about the workings of private schools to postulate whether this theory holds there as well.
Despite the fact that Hillary Clinton didn’t shatter the glass ceiling in 2008 (although, it’s hard for me to imagine how 18 million cracks would not shatter a glass ceiling, but that’s a separate issue), women have made extraordinary progress the past few decades. Intelligent, motivated, and accomplished women who at one time would assuredly go into teaching are now going into other professions that were previously more difficult for women to enter. The result is that, on average, teachers are of lower quality than they had been in previous generations.*
*This is a big picture argument. Admittedly, the recession may lead more qualified individuals to go into teaching or to do Teach For America for two years, but my theory concerns the overall quality of public school teachers.