If one wishes to understand what is essential for learners to know in order to read and write English, this is the book. Although its topic is English, its insights about all languages are profound.

Although this book can be hard to read (i.e. it has a rather academic style), it's well worth the effort. Gattegno presents ground breaking insights into education and how to best subordinate teaching to letting students learn a language. Any one who teaches languages or who wants to learn one efficiently, should read this.