In teaching we have too often simply lowered our standards. If keeping were spelled with a 'c' my points would be even easier to remember. We must make the profession attractive to the young people we want teaching our children. The most efficient recruiting engine we will ever have is the cadre of enthusiastic, well-prepared high school science teachers. Recruitment of teachers is hindered by exactly the kind of things that cause teachers to leave the profession.
Counter examples abound.
I was there. Teachers must be assigned to teach only courses for which they have sufficient preparation. Science teachers must have real opportunities for professional development and scientific education. We will likely recruit more science teachers by collaboration with the colleges of education than any other way. High school teachers - university and college professors can collaborate with highly qualified high school science teachers who can then offer courses for elementary teachers wishing to becoming science teachers.