Funny how this distinction specific to social studies is also found in high school biology and sex education classes. One would think that being taught this distinction in school would make it common knowledge. I wonder what would result from an Internet search of sex vs. gender.
Interesting you should mention political agenda. I have a suspicion that the deliberate mis-use of gender for sex might have been a matter of political agenda, but I haven't yet researched the evidence for that aspect of my argument. Another thought was that it started as a euphemism for sex by people who were uncomfortable saying sex. Again, I have yet to research possible origins.