My father was a flight instructor in WWII, and had both male students (1942) and WASP (female) students (1943-44). His comments were that the washout rate was about equal - and both M and F in general could use a little more solo practice before graduation. He had particular praise for a few of the "girls" who were quite proficient.
Incidentally, he never had any ambition to become a CFI after the war. He was, however, a valued resource for the instructor community, and occasionally tutored a "problem" student - especially in what he called "confidence building" -
slow flight, pattern and landing work, ...