Sheeplikessleep" - no, because in your son's case, his difficulties are not attributable to language exposure. The interaction is between what a child can* do (their basic abilities) and what happens around them. Often, children with significant gaps between their understanding and spoken language/speech have underlying difficulties that prevent them from gaining maximum benefit from general language models around them e.g. working memory issue that mean they can't hold onto words in their memory long enough to extract ALL the information they need to be able to understand, use and articulate the word. Or they may have a motor issue that means that articulating the word is hard which then reduces their access to this word in spoken language. It's a complicated, individual thing.. so they may need an altered input e.g. to listen to the differences between sounds at an individual level or practice these sounds at an individual level to help their developing linguistic systems.
SuchProspects, I am a bit ambivalent about the Hart and Risley study - I think it probably is ethnocentric and its methodology was overly behavioural/simplistic/too small a sample size.
However, all research can be criticised and the reality is that any of us working with poorer students in educational settings can see pretty clearly massive differences -between the language and communication of children from different socioeconomic backgrounds that effectively lock poorer children out of learning and contribute to the cycle of disadvantage. Yes, there are undoubtedly broader issues at work here with reference to how the curriculum is structured in such a way that it denies the experiences and communication styles of the many to give preference to the few... but what I am faced with on a daily level is kids who just can't access the language of the curriculum at all and even if this reflects some grand sociopolitical truth about the disenfranchisement of the poor, my job is to help them understand those words and sentence structures so that they can actually participate in their day to day lives/acquire skills that society deems valuable in the workplace. Does this mean teaching poor kids how to understand and use middle class language? In our current context, probably.
The kids I work with obviously have other issues.. bigger fish to fry.. but when observing in regular lessons I see bright kids who have difficulties repeating words like atmosphere and metamorphosis because they are taught rapidly and without linking them to a student's prior knowledge base so their representation of the word is fuzzy. They are culturally decontextualised which means they are linguistically hanging out there on a limb and even those children who remain motivated in the context of an uninspiring curriculum with no relevance to their own cultural identity struggle to do something as basic as repeating the word.
If much of your language exposure at school bears no relevance to your experience or is pitched at a linguistic level which you have not had cause to develop at home, it is highly likely to make you zone out and reduce your participation in the language around you.. which will make it harder next school year when that language has become increasingly more decontextualised and irrelevant. For some students, I do believe this actually impacts upon their linguistic development because the time they could be spending engaging in any meaningful language activity (not just one deemed appropriate by a middle class person or Whitehall) is being wasted. Much as if a healthy person lies in bed for weeks, their muscles will waste...
I don't think it's as simple as some sociological commentators would have it, that there is no fall out from differences in exposure, it's just that people assessing them use middle class tools to judge and disempower them. My colleague who worked with a very poor, multiethnic inner city Youth Offending population used standardised assessments on all of them to establish a baseline, and found that about 70% scored well within normal limits on these measures even within a skewed population. So the tools must have some validity as a measure of language development, despite being perhaps too "middle class" in terms of some vocabulary items/structures. Why the rest of the sample scored below normal limits (when a middle class population would only have about 2-6% depressed scores) can't simply reflect ethnocentric bias. I'm not having it that working class people are simply "thick" so if it's not language/word choice and it's not underlying cognitive ability, there must be an environmental explanation.. I am happy for that to be that the educational system reduces opportunities for development as it is not culturally sensitive enough, but I am not happy to simply believe that if we all just try hard enough to be "right on" that the reality of educational and social disadvantage will disappear.