If the Prussian model is soooo spectacularly wonderful, then you have nothing to fear from it being exposed to a competitive environment. It'll win. No worries.
On the other hand, if the Prussian model is, shall we say, less than optimal for the 21st century, the fastest way to find out is free market experimentation, and rather than giving ourselves the same cultural shackles that everybody else has, the American exceptionalism that will justify our salaries will be our willingness to experiment, learn, and refine from there where everybody else insists on the Prussian model. Unless, of course, a 19th century schooling model is just so damned perfect that it will admit of no significant improvement. In which case we'll still find that out pretty quickly. The maximum downside is sharply bounded and the upside of cracking open the monopoly on education is hard to bound. (I can't call it "unbounded" with a straight face, that's hard to justify, but it really is hard to know how much better truly 21st schooling could be.) Failing to at least try some innovation isn't even remotely justified with a cost/benefit risk profile like that.
Had some other country beat us to the punch and exposed their schooling system to free market competition before us, we really would be up the creek without a paddle.