A nice, short, simple book that covers the essentials any interested person should know about how children learn music.
My (overly simplified) interpretation is as follows. Gordon asserts that music appreciation and achievement are related. Thus, if children improve their musical skills, their appreciation of music will improve also. Given this, how to teach a broad learning sequence of rhythm, melody and harmony is described. Generally, the message is that children must first develop their aural skills before they are 'ready' to engage with notation.
I look forward to properly diving into Gordon's seminal work 'Learning Sequences in Music' (which this book was the precursor too) to see if Gordon is more explicit about the age in which concepts, and teaching methods, should typically be introduced. Specifically, I found it interesting that the latter end of the book talked about part singing, suggesting that two-part singing is typically introduced to fourth-grade children (aged 9-10) in practice. Nievley, I assumed this age was too young for children to have developed such musical sophistication - particularly, in a classroom setting. Hopefully, 'Learning Sequences in Music' will better support my understanding of this.
Overall, the book is very short and, thus, readable in one sitting. For this reason, I would recommend 'How Children Learn When They Learn Music' to anyone - students, teachers, researchers, hobbyists - with an interest in childrens' skill development in music.