The average height of the staff here at the Curmudgucation Institute is about 4.5 feet (the Board of Directors really pulls the average down). Yet if you buy clothes that fit a 4.5 foot frame, those clothes will not fit anyone here.
The average guy named Peter Greene has made at least one major film. And yet, here I sit, with no IMDB entry or residual checks coming in for my work.
So here's one reason that a lot of educational research is that it is the findings are about average students. And nobody teaches an average student. Each student is a very specific individual with a specific complex of specific characteristics, strengths, weaknesses, history, etc.
So something like the widely-circulating NWEA "research" (aka "wild-ass guess") about the Covid-19 slide that everybody is kind of expecting to be a major feature of school in the fall. And really, three's no reason that the testing company can't make an edu-WAG; right now, WAG is pretty much all anyone has. But from a classroom teacher perspective, I have to ask what earthly good aa piece of research like that could be. From the classroom perspective, it boils down to, "Each of your students will be 'behind' some amount, more or less."
This is the problem with much of the "science" out there about learning--it describes what the average student does. But if I'm in a classroom, I don't want to know how the average student leans about widget decoding--I need to know how I can best get it across to Pat, who has a short attention span and not much interest in the printed word but likes to draw pictures all day, or Chris, who is pre-occupied most of the day with dinosaurs, and who doesn't read long multi-syllabic words easily, but who never forgets anything you read out loud.
One size does not fit all, but average size doesn't fit anybody.