Two recent papers, one from University of Maryland and California State researchers Sean Corcoran, William Evans, and Robert Schwab and the other from Caroline Hoxby, a labor economist at Harvard, explore the factors contributing to a marked decline in the quality of the teaching force over the past four decades. Both papers document the fact that women have better job choices than they once did. Hoxby adds a particularly useful, less recognized insight, suggesting that there is a more important dynamic, impacting teaching quality: the compression of teacher compensation as a result of increased teacher unionization (stay with us!).
Hoxby illustrates that the percentage of high aptitude teachers has declined significantly over the past five decades and attributes this decline, in large part, to the increasing homogeneity of wages as a result of collective bargaining agreements. In other words, collective bargaining has resulted in fewer really high wages and really low wages: over time, wages have migrated to the middle. In fact, she is able to conclude that wage compression is responsible for about three quarters of the decline in teacher aptitude. While she does not dismiss the impact of increased opportunities for women, she maintains that the trend only partially explains the disproportionate decline in the category of high aptitude female teachers.
Both papers take on a difficult issue that warrants far more space than we have here, but they're both worth a full look.