It's the truthiness of the concept, though, not really whether or not it is real. Ergo, additional evidence is no more important than it is to religious observance. The entire construct is belief-based to begin with.
I'd also argue that this is a shining example of something else that I've noted to be fairly endemic in education (as a field, I mean):
if you WANT it to be true, just believe it hard enough. Voila!
Please note that this also explains why some educators truly believe that acceleration is harmful (in spite of reams of decent quality evidence to suggest that at worst, it is no MORE harmful than doing nothing), and the like.
So many, many studies in the field are so poorly constructed that they are more or less meaningless, and there is also a very hefty dose of engineering experimental design to generate the desired outcomes. Add in a hefty dose of chutzpah (at least I think that's what it is... though maybe it's ignorance meets hubris?) and you get pronouncements that literally make NO SENSE in light of the data in the study.
I've actually seen classroom educators read such a study and nod sagely while pronouncing that said publication "supports the classroom practices*" that they have been using with "good impact** on learning."
Perception as reality, as my DH would say.
* Bogus classroom practices, at least if the data in front of them in the publication is reliable, that is.
** How this is measured isn't ever quite clear either-- I guess they FEEL that students are, er, well-- better somehow. It makes them feel effective.
Elementary educators tend to be very predominantly of this type.
