With career and employment alternatives increasingly available, one might think that fewer women would enter occupations and professions that traditionally have been predominantly female. This has not happened for teaching. Both the number of women entering teaching and the proportion of teachers who are female have gone up….It is unclear why this has happened.
To add to the Ingersoll et. al. comment above, this is a period in which women have seen some improvement in wages relative to men outside of teaching, but not as teachers.
P.S. In private schools, the fraction of women teachers has declined. The change is about 4 percentage points over the same period.