In my research report – I have data going back to mid-1800s about percentage of male teachers. The numbers started decreasing because of the changes in demographics of women:
1) Delayed marriage;
2) Delaybed childbirth;
3) Increased education for middle class women.
The percentages had a small increase during World War I and then again during the Great Depression. We saw a significant increase after World War II with the return of veterans and the GI Bill funding soldiers education.
You can find the source data in the Educational Statistical Abstracts. The books aren’t easy to find – I was able to access them during my graduate work at Harvard University in the basement of their library.