Whimbey and Linden review an assortment of frequently-used pedagogical techniques for teaching writing in America (including WAC, which was and I believe is used in the Hingham Public School systems), discusses their history, and attacks most techniques as ineffective. As an alternative, they introduce the techniques of sentence-combining (SC) and text-reconstruction (TRC).
I disagree with another reviewer that the book is merely an advertisement. While they do mention Whimbey's work frequently, there are a few problems with this facile classification. First of all, both SC and TRC can easily be replicated without Whimbey's books. I plan to do this at both of my educational jobs. Second, the book is clearly trying to inform teachers and administrators about the failings of pedagogies like WAC and process writing, while advocating for their replacement by SC and TRC. While Whimbey surely stands to profit from the spread of SC and TRC, I wouldn't be surprised if his main motivation was trying to fix America's problems with reading and writing. Forgive me for being too generous if he is more selfish than that—I got a lot out of the book myself!