The article takes a look at some of the recent ideas about a child's language environment and how the language used around a child might influence their vocabulary and understanding. It also includes a checklist of some simple words that most children would be using by the time they're 2 years of age.
The 15-year project followed 40 children from privileged backgrounds who were diagnosed as late talkers but were otherwise developing normally.
While most of the children had caught up and developed an average range of vocabulary by four or five they remained slightly behind peers from the same background in vocabulary, grammar and reading throughout their school years, suggesting that their late development of speech had put them at a disadvantage.
The word test devised by Prof Rescorla can be completed in ten minutes and doctors can tell at a glance whether a child's speaking ability is poor for their age.
Personally, I think it discriminates against yokels from Norfolk who would not know many of these, but would probably be able to label several types of tractor.