Not only that, but doubling the pay of teachers will only improve your results if you get rid of your current teachers. Which will be difficult to do. Otherwise you are just paying the same people more money and probably getting the same results.
It's very hard to get to a social change to pay them like Singapore.
I think the means to this ends is via charter schools. Parents know who the good teachers are, and they fight to get taught by them. Charter schools have found a way in some cases to pay up. I think parental voting (with their feet) can be even better than test-based metrics, which are imperfect at best. (Everything not on the test gets neglected)
This is a very complicated problem.
Standardized testing implies you really have to nail the test design, and be vigilant that people aren't working just to the metric, and aren't cheating. (Freakonomics has a chapter on how they caught cheaters in Chicago. Apparently they caught them in other cities too but didn't have the courage to fire them elsewhere.)