Most Americans don't even know what Common Core is. But they should. It's the government's plan to try to bring "the same standard" to every government-run school. This may sound good. Often, states dumb down tests to try to "leave no child behind." How can government evaluate teachers and reward successful schools if there isn't a single national standard? But when the federal government imposes a single teaching plan on 15,000 school districts across the country, writes John Stossel, that's even more central planning, and central planning rarely works. It brings stagnation.