The book's coverage of spelling is both enlightening and thorough. Teachers of all types of English, from primary school to ESL and EFL will be well served to study the insights the book provides. As just one simple example, I had no idea why certain words with the /'/ sound were spelled -ge and others -dge, but the book provides a simple explanation that could be taught to struggling students as well as plentiful activities to use them.
For adult ESL learners, however, the book still leaves gaps. It relies on students being able to distinguish between sounds that many non-native speakers have trouble hearing in order to make spelling decisions. In particular, the short/long vowel distinction (which is a central component of almost every chapter) is notoriously difficult for learners whose native tongue is Arabic, Japanese, Chinese, or even Spanish. The /e/ sound (as in "rate") and /æ/ as in "rat" might seem obviously different for us, but for many of my students, perceiving that difference, let alone producing it, remains an issue. It seems that, in order to make full use of this book in my setting as an adult ESL teacher, pronunciation exercises might need to be a necessary prerequisite.
Still, for native speakers, this book will provide a great deal of useful information, and for teachers of all levels, it will provide some semblance of order in what is otherwise a chaotic, idiosyncratic spelling system. Highly recommended.