In 1940 55% of college educated female workers in their thirties were employed as teachers.  As opportunities  for women broadened the best and the brightest left teaching and went into other higher paying fields.  The school teaching profession experienced a brain drain.

“In 1960, about 40% of female teachers scored in the top quintile of IQ and other aptitude tests, with only 8% at the bottom. Twenty years later, fewer than half as many were in the top quintile, with more than twice as many in the bottom.”

“Between 1967 and 1980 U.S. test scores fell by about 1.25 grade-level equivalents.”

From “Superfreakonomics” by Steven Levitt and Stephen Dubner

HKO comment- unintended consequences, ain’t it a bitch.