Let me tell you that trying to fix high school is hard and, almost in any case, impossible. You can't fix high school and ensure that it's environment is as productive as the one that can be found on college campus. It's simply not doable. Even though teachers aren't getting paid enough, there's a much bigger problem:

Sociological problems. The worst kind of problems. Negros and Latinos come from troubled neighborhoods and families. The thematic of neighborhoods talked a lot so for reasons of brevity let's not talk about that. In terms of families!, things just don't look great. A lot of minorities had the institution of marriage destroyed and by that graphic a lot of kids are being brought up into families of dubious quality - less family members equals less attention. They just don't have a healthy emotional life and without that it's hard to actually give a crap about school. And this is coming from someone who had two parents, but for 6 years all they did was threatened each other with divorce. I suppose it's a lot worse by not having something you can call a dad or a mom and having to find a role model in a thug environment.

What am I trying to say with this? I'm saying that fixing high school isn't going to do much. Teachers only can help to some extent. The real issue is a racial (or ethnic as you prefer). So, this is why no one wants to talk about minorities, because no one wants to talk about races, cultures or whatever is related to this problem. People are afraid of even doing so. This is why Sanders prefers to talk about college, because you only need to do tax reforms and "bam, done".