Disclaimer: I'm not experienced enough to suggest changes for the overall system; I skipped from second grade to college, with a lot of homeschooling between. That said, I'd suggest, at least for a lesson system, khan academy's method.
Khan Academy is an online school which teaches math and other subjects such as medicine, finance and economics, all through pre-recorded videos. The videos are comprehensive, and easy to learn from. They're also designed such that a teacher can essentially use the videos as a lesson, and then personally help any students who might needassistance.
The primary reason I like this system is because it can be used as the lessons, and places a teacher in more of a personalized help role, rather than a outright teaching role. In college, I've had many different teachers, of many different skill levels; Some were, frankly, incompetent to the point of occasionally teaching incorrect information. Others were very good, and made their subject interesting without compromising the information they taught. One of my best teachers taught political science through videos... which he had made over a year ago--he was reusing them. He could spend the entire class personally helping people, and we could review the lectures on our own after we got home.
If this became a primary method of teaching, teachers could simply use the chosen videos for their subject, and be trained on how to assist students who need help, along with the standard role of grading things. That would mean that all classes would effectively be taught by the best teacher in their subject, so harm caused by poor teachers would be minimized. Furthermore, the videos can be revised and improved with feedback from all the classrooms using it (2); A traditional teacher can only improve their teaching using feedback from the few classes they personally teach.
Oh, and the U.S. Department of Education is currently studying how effective Khan Academy is at teaching. They funded a several million dollar trial to examine how effective it is at teaching math, back in July 2014 (3).
Links, because I don't know how to make reddit link things:
(1) https://www.khanacademy.org
(3) http://ies.ed.gov/funding/grantsearch/details.asp?ID=1521
And one more, an article by a Wired writer who's far more skilled than I: