Education and an usual side-effect of opportunity

How much of the claimed declines in US academic performance/quality of education is a result of MORE opportunity for women and meritocracy?  When there were more and higher (not that there are none today) barriers to women entering the workforce, how many women became teachers who, today, would be high-powered lawyers, doctors, etc.  And thus were able to provide exceptional educations because they were actually over-qualified (or, given that teaching standards are usually quite low, more qualified than demanded by schools but actually the "right" level of qualification).  Of course, this doesn't explain all the gaps in education (some Scandinavian countries have very high quality of education but a very egalitarian society) - but it also seems to play a role.