What was needed was new, more sympathetic examination of the culture of apparently inadequate groups. This in turn meant new methods of enquiry, using methods borrowed from anthropology. These involve participating in cultures and observing them, trying to understand them through the eyes of the participants NOT imposing your own value judgements. People are not deprived of culture, but simply have a different one. Maybe the best example is the work on language.
Linguistic deprivation is perhaps the best argument to link social class and underachievement.
It is a very commonly found and popular explanation of underachievement, often rendered in a rather simplified way. Labov, a linguist, argues that this just does not sound like human language at all. All humans are and must be capable of complex speech, all can use it to escape context and express general concepts. It is just that we express ourselves in different variants of language. Apart from the issue of cultural prejudice or bias, the answer was really an obvious one - people only use complex speech when they feel at ease, when they feel the listener wants to know what they think.