Leaving aside the merit of that claim, we need to ask who should do the teaching. The duty of serving is a matter of morality, and that is the province of the family, not the schools. Parents typically want their children's schools to encourage virtue. But we have a problem when it comes to the government's schools. Because those schools are financed by taxation and filled through compulsory-attendance laws, they are virtual monopolies.
Most people have to send their kids there.
Now we are talking about imposing particular moral lessons on children, perhaps against parents' wishes. That's wrong in a free society. The answer to the monopoly problem, of course, is to separate school and state for the same reasons we separate church and state. We don't want the state to be our pastor. If it must do something, let it do no more than keep the peace, so that we may each pursue the good life as we see it.