The book is an easy read and short enough to be read in a day. It could be considered a philosophical precursor to "The Book Whisperer" by Donalyn Miller. The language is quite dated, but the underlying pedagogical philosophy includes things like making learning fun, meeting kids where they are (differentiated instruction), and free reading, all of which are are still applicable today.
(reaction written in 1976) This is the most convincing manual for teaching I have yet to see. The message and technique are difficult and take a lot of dedication, but Mr. Daniels has convinced me that they can work.