The early work especially seemed to offer a neat chain of argument to connect home background, language and cognition, and educational success.
Language is a cultural matter, a way of expressing meanings, of coding experiences.
If your experience was of a particular type, so your language would code this experience in a recognisable way. Language is also a technical device to express not just culture but knowledge, including school knowledge. Then school language should also be able to express these qualities - be flexible, rational, abstract, and have an elaborated grammar and syntax to permit elaborated arguments to be coded. If we go along with all these assumptions and suggestions, we have a neat 'linguistic deprivation' theory to explain w.c. failure. Rosen argues the same points could be applied to British w.c.