I think it's just typical psychology bollocks. Cursive is faster to write, but much more difficult to read, especially if written by someone's else. So with cursive you can write down more and if you just assume that the more you write the better then you arrive at the 'obvious' conclusion that cursive is better for the cognitive development. I guess it all comes from the very old school of teaching where during a lesson a teacher literally dictated a paragraph from a textbook and the pupils carefully transcribed what they heard into their notebooks.