This book comes from the Hanen Centre in Canada, a foundation which for over 30 years has developed parent courses as a way of providing therapy for children with language development difficulties. The book accompanies their parent course of the same name, which is often run by speech and language therapy departments in the UK (& Canada & the US). The course gives parents additional insights into how to put the strategies described in the book into practice, and a key element is the use of individual video sessions so that parents can see how their child responds to what they try.
A tip for those put off by the price - the UK distributor, Winslow Press, sells new copies of the book, and also the accompanying DVD, at a more reasonable cost."
The website for Hanen is http://www.hanen.org/ the store is pretty good, but the information is limited.
Try the book More than Words... here: http://www.amazon.co.uk/More-Than-Words-Communication-Children/dp/0921145144
WIKI is a little more detailed - http://en.wikipedia.org/wiki/The_Hanen_Centre
It seems that the use of visual supports are promoted a lot with Hanen, which obviously is something that we have succeeded with and feel strongly about.