Hey Higher Ed, Why Not Focus On Teaching?: http://www.npr.org/sections/ed/2017/06/07/530909736/hey-higher-ed-why-not-focus-on-teaching
Nobel Prize winner Carl Wieman, author of Improving How Universities Teach Science: Lessons from the Science Education Initiative, advocates the use of active learning in college classes. This seems to me to be a great idea as it would not only help teachers learn the subject matter but also have experience with active learning. He says that many K-12 teachers come to college without the needed science knowledge to teach the classes they are assigned. I don't know about high school, but I have found that many PreK-middle school teachers learn as they teach. Having a depth of knowledge beyond what is taught at an assigned grade-level and experience with active learning would make classes more effective, it seems to me.