A real comparative-historical account of the different branches of
the tree would be fascinating. Arne Raeithel did some of this several
years ago, and Alfred Lang has done some, and Bud Mehan wrote about
different forms social constructivism, but I know of no place where
a really comprehensive comparative treatment has been given
mike
Ps- Yrjo also has lots of good material in learning by expanding,
now a bibliographic rarity.