My wife and I have been in education since the mid-70s in three states.

At least in our experience, the key to the teacher shortage is clearly to make the job more attractive:

1.) Working conditions on all levels...counselors, safe schools (no guns), respectful administrators, time to prepare, etc. Many schools today are war zones - and who wants to work there!?!
2.) Quit siphoning all the good kids to for-profit, charter schools and leaving the poor, special kids crowded into an under-funded, left-over schools.
3.) Teachers need MORE preparation, not LESS in today's schools! Once you get past the content, the hard part is dealing with classroom management, special ed., legal issues, new technology, and testing. Uncertified teachers drop out like flies and require constant mentoring. The Superintendent is wrong (been there, done that)! Less qualified teachers mean a weaker school.
4.) Pay and job stability are making teaching one-step above minimum wage. Well prepared teachers start with a college degree, but the better ones almost always have a graduate degree, years of experience, multiple certifications, and really care about the profession. Depending on your particular state or district, pay is well below other college educated professions.

Teachers need to be paid far better than they are currently being paid.