We chose this book and it has worked very well. 

For a motivated older student or adult, this is a great choice. 

I believe a basic understanding of music is necessary to be an educated person. Our goal is for Caroline to be able to read music, understand basic music theory, and play pieces on the piano. How far she goes with it will be up to her. She will, at the least, have the tools to understand music discussions throughout her life. 

https://amzn.to/4tnuyfQ