I've never had to deal with sexism. When I was bullied in high school my car was vandalized, I had to take time off from exams because my face was a wreck and I was being monitored for brain injuries. I skipped class because I didn't want to hear, "fag," for the thousandth time. I didn't want to deal with the food being thrown at me in the cafeteria or the snickers as a I walked past the gossiping kids in class. I've never had to deal with being discriminated against because of my gender but I cannot imagine that it hurts any less.
I was lucky. A friend of mine was beaten into a coma. The bullies showed up to his benefit concert to throw pennies and harass the attendees. He has been living the rest of his life with the effects of severe neurological trauma. Yeah, kids are mean.
It has been more than a decade since I escaped that hell-hole. I've since read articles about other unlucky kids who've died being stabbed to death by a mob. I've read about girls who have committed suicide because they couldn't deal with the slut shaming. Sure these cases are beyond the norm but I wonder if they are not indicators that things are just getting worse for kids these days.
It doesn't have to be this way. We can single people out who make sexist jokes and correct them, loudly and publicly, and try to help them understand that they're not funny, clever, or cool. I agree with the author that teachers can be a part of the solution. But I don't think that is the final word (and it never is when trying to change prevailing attitudes and norms): parents need to tell their kids to stick up for people who are being bullied, that it's not funny, and that it's dangerous to not say anything when they hear someone spout off something hateful.