the park city programs in summers are excellent opportunities to meet and interact with high school teachers. I am also impressed with "the wisconsin idea", that university research should affect the lives of the community. They have an outreach department that does more than cure corn blight, and actually communicates with local school teachers. I hope this idea may take hold here in my state, where we have a top ranked university math education graduate school, but poor quality math education overall in our pre-college school system.
Twenty years ago or so I also volunteered to teach advanced calculus at a local private high school. We used the book by marsden and tromba and it worked well for those students ready for it (most of them). I wrote a summer proposal into my NSF grant to fund these students, a few other younger ones, and their teacher Steve Sigur, to be paid to go through Mike Spivak's appendix to his Calculus (on the real numbers, rigorously) with me, while I again volunteered the free month of my summer for this. One of my students was Jeff Brock, now a professor at Brown in topology. Another of my students, Jonathan Manson, became a Phi Beta Kappa in physics at Harvard, and took a PhD at Illinois. Another student went to Chicago and took the Spivak calculus class there.
I also monitored the students in preparing various math projects, on Galois theory (that student went to MIT and is now a math teacher at a private school), cyclotomic polynomials, and Mandelbrot theory and eigenvectors.
When my son was in second grade I colored the faces of some polyhedra and gave a lecture to the kids on the relations between vertices edges and faces, and one little girl (who later became an aeronautical engineer) guessed Euler's formula.
You can do a lot as long as you are willing to volunteer your labor. It would be nice also to earn some income at this, but that seems harder. From my experience, although funding is minimal for high school students, that is precisely when you need to magnetize them to mathematics, or they may be lost forever. It takes real persistence to keep loving math through 12 years of boring instruction.