If you were in the American slave-holding South in the days of slavery, and a supporter of slavery was demanding studies and ‘evidence’ to justify your argument for ending slavery, would that not strike you as a highly immoral stance?
In this heyday of scientism, all sorts of experiments are performed to back up every conceivable view of education, and people simply cite the ones that confirm their prior beliefs and ignore the rest. Hence they are asking other people to abandon their opinions in deference to a type of ‘evidence’ which they themselves would (quite rightly) not pay a moment’s attention to if it had gone the other way.
One of our best theories (the framework theory of evolution) is not scientific, but that it is none the worse for that. And all scientific theories rely on a philosophical framework.
No sample can be large enough to control for all the variables in any experiment involving human psychology, because the variables include the ideas in people’s minds, and he number of possible ideas that a single mind could hold is far greater than the number of people on Earth.
There is no point demanding testability of an educational theory. What one can do with philosophical theories, is refute them by argument. Empirical testing is just one of a number of types of intersubjective criticism, and the vast majority of all criticism is by argument, even in science. Most scientific theories are refuted before they even get to the stage of empirical testing.