Learning is, in general, NP hard. But some problems are easy or easier. There may be a temptation to simply use education research to identify the easy subject matter (and methods) and then only teach those topics or those examples. This is likely to prove popular with the student community and administration. We might then end up only teaching classical (e.g. Newtonian) physics, for example, and neglect harder things like relativity and quantum mechanics. The difficult foreign language courses have disappeared from many colleges.
I see no problem with identifying and starting the students off with the easier material. I just want to be sure that we eventually cover important subject matter even when it is difficult.