I agree with Adam, but I'd also like to say that many of the groups find their own niche. It may look like there's a lot of overlap, but they actually do find their own little specific field that's important.
As the many educators in the room can attest to, every classroom is different and every learner is different, from the youngest child to the oldest learner, and each group is very good at finding that way to get through, that way to break through. I think it's important that we come together to find the best practices, yes, but we also have to allow the teachers in the room and the people writing the programs to do what they do best.