Agreed, Mrz. But we've been trying for a long time to target this 20% of parents, to help them change how they interact with their children, and it hasn't really worked very well. That was one of the problems with Surestart, that it wasn't reaching the target group, who are often suspicious of getting involved in anything "official"; instead it was being used by large numbers of middle class parents.
From the article: “The problem of poor early language and communication skills is much more prevalent among lower income families where perhaps the parents might themselves have struggled at school.” Also, If parents themselves have limited vocabulary (as suggested by the Hart Risley study), or have other problems such as mental health difficulties or addiction, that too could contribute to them not being able to provide the desired language-rich environment.