This book combined easy stuff I learned in band starting in 4th grade with stuff not covered even after I majored in music.
As an instrumental person, I learned notes and scales before we focused on rhythms. It was interesting forcing us to see and read both the major clefs: treble and bass. Some rather odd mnemonics to learn the lines and spaces. As a flute player, I didn't even know there was a rhythm clef. I did learn somewhere along the way about the C clefs: soprano, alto & tenor, but I never had a use for them myself.
Major and minor keys of course, even modes: Ionian, Dorian, Phrygian, Lydian, Mixolydian, and Aeolian, okay. Just don't ask me to explain or play the modes. And then be really loses me when he gets to blues scales, bebop, Persian, Insen and Super Locrian. I can cope with whole tone scales: there are only 2 and I use them to warm up. Seeing the pentatonic scale is cool though.
He gets into chords and chord extensions, which are apparently of use in jazz. I play a melodic instrument and not much jazz, and don't get much into chords.
He gets back into my ballpark with double flats, even double sharps (more of use in orchestra than band, for flute at least). The weird time signatures are familiar from much of the music I've played: 5/8, 7/8, even 11/8 and 13/8. They're sometimes fun and it's always entertaining watching the conductor for these.
I do like that in the quizzes for each section, he gives the answer and page number to go back to if you're stuck or just fuzzy on some concept.
Each chapter has a quote at the beginning. I really like a quote from harpist Wanda Landowska: "I never practice. I always play." In other words, even in the practice room, always make music. Even with scales. Even with rhythm practice.
Other quotes come from Louis Armstrong, Charlie Parker, Benjamin Franklin, Rumi, James Galway, Thoreau, Nietzsche, Stravinsky, and many others.