First of all, an effective teacher must have knowledge of the subject. When I started teaching, you needed three years beyond the learning level to teach a vocational subject to obtain a provisional license. Under the REPA II you would need to graduate college with a decent GPA, and pass a test to show your mastery of that content area and you get an adjunct license. Not really sure about the license part of it but it's not essential to the conversation. The biggest thing, and one of the few things that everyone seems to agree on, is the need to have a mastery of the subject.
Second of all, you need to be able to impart that knowledge to the little darlings. Lots of ways to do that and lots of ways to fail. You can use lectures, demonstrations, technology such as Power Point, guest lecturers, team teaching, and increasingly, long distance/computer learning. Lots of presentation methods available, which is good because people learn best in a variety of ways.You also must be an entertainer. You've got to capture and keep the students attention so you can dispense the knowledge.
Does that really require a teaching degree? I don't think so. At least not as they are now. The old vocation license route coupled with a skills test pretty much would insure that a teaching candidate knew his beans about his trade. If you take the regular education degree route, you really don't spend a lot of time on your specialty. Maybe a half dozen classes on your specialty, let's say math at the high school level, and the rest of the time is spent on teaching methods and elective courses of some sort. When you are all done you're considered an expert on math but are you really? Likewise, are you an expert teacher? Every one has to student teach but does that make you an expert? Once you're in the classroom on your own, you find out pretty quick what the teaching profession is really like and it's not necessarily like the student teaching experience.
When they place a student teacher, typically it's with a really good older teacher. Makes sense - why would you want them learning from a slug? However, by doing that, you put the student teacher in a class that the older teacher has already groomed. Most behavioral issues have already been resolved, the room is fully functional - there are enough chairs, the computer works, there's a pencil sharpener, the bulletin boards are decorated - so there isn't much that needs to be done except show up and prepare for the day when the older teacher lets you fly solo.
When you get your first teaching position, things change quickly. You're suddenly surrounded by a very diverse group of students who you have to somehow convince to sit still long enough to solve for "y" when "x" is 17 and "z" equals 15. And as if that's not challenge enough, then all the crap that has absolutely nothing at all to do with being a good classroom teacher comes into play. Now you have lunch room duty, bus duty, meetings before school, meetings after school, hoops that need to jumped through to renew your license, club sponsorship, school improvement committee membership, or if you're a welding instructor, fix the piece that holds the high jump cross bar because there's a track meet in 15 minutes. So when you could be grading papers or preparing a lesson, you're standing out in the parking lot in the rain until the buses have all the kids loaded up and start their routes or try to reach a parent on the phone. And then, come payday, you wonder how in the hell you're going to pay back your student loan when your $28,000 per year salary barely covers your living expenses.
I truly believe teaching is a calling. All great teachers have a gift. If you know the material and have the gift most of what you need to be an effective teacher you already have within you. You need some pointers and a chance to try it out without screwing up someone's education, of course. But do you really need an education degree? The Great Courses have The Art of Teaching: Best Practices From A Master Teacher (24 lessons, 30 minutes each). It's on sale now for $69.95 plus shipping. I'd be willing to bet if you gave that special someone with the gift within them the DVD's and some practice time before a live audience as long as they knew their subject well, you could probably turn them loose in a classroom with excellent results providing they get some help as they're getting their sea legs.
When I was a rookie at the steel mill, they put a red stripe on my hard hat so everyone would look out for me and keep from hurting myself or someone else. I remember the one motorcycle racing organization I belonged to did basically the same thing. Rookie riders had an orientation and wore a bright yellow vest to warn the other riders. Maybe something similar for rookie teachers. A bright yellow blazer so all the rest of the teachers would look out for you. As far as many of the students go, they're going to paint an invisible bulls-eye on the rookie teacher any way, so the blazer wouldn't effect them much differently.
So then, you want good teachers? Here's the prescription:
Start with people who know their subject matter and have the gift.
Have them watch the Art of Teaching course or something similar.
Have them practice their teaching skills before a live audience prior to entering the class room.
Provide real leadership and support in the schools.
Pay them a decent wage.
Let them teach their classes in any way, shape or form they wish. Give them the autonomy they need to accomplish their task and then get out of their way.
Stop all the rest of the foolishness that just saps their energy and gives no educational return.
It could all be so simple.