Limiting Factors

Somebody asked online about some research their principal had just heard about that said " reading aloud to children does not improve reading, but that having access to lots of books is more influential as a factor."
I found myself rending the hair and gnashing the teeth... and then wondered why these people have this compulsion to look for THE ONE FACTOR.
My bachelor's degree is in Wildlife and Fisheries. In my first ecology class, we learned about "limiting factors" in population growth. To coin a phrase, "if it's not one thing, it's another." If a population is going to grow, whatever is the limiting factor has to be addressed... and once that is addressed, the next limiting factor will take over at a certain point.
Oh, and the limiting factor for one population isn't going to be the same as for one population as the next. It might be the climate in one place (Alaska) or predators in another... and of course, it'll be predators for the field mice but having enough space for the grizzly bears.
Educator types, please try to understand it's not about The Missing LInk. What are your students' limiting factors? By focusing on the biggest one *only* you might be opening one gate... to have another closed one two feet down the road. And, of course, if you're opening the gates down the road, but the student isn't past the first gate, s/he'll never know.
Just a thought :=)