The following errors have been noted in the first printing of RFZ. You can print the corrected version by clicking on the appropriate hyperlink:

Teacher's Guide, Lesson 1,1: "Cleff" should be spelled "Clef"
Teacher's Guide, Lesson 1,1: add the following text after "even without the": "recorder, just by keeping your lips together loosely while blowing."
Teacher's Guide, Lesson 12, 58: "Rhthmn" should be spelled "Rhythm"
Lesson 13: #70 - key signature of one sharp
Lesson 13: #70 - measure 3 in the soprano part is missing two quarter notes
Lesson 13 #72 -  next to last measure on bottom soprano part should be quarter note e instead of d
Lesson 16: #85 -  measure 7 in the alto part is missing a quarter note d and an eighth rest
Lesson 16: #85 -  measure 9 in the alto part is missing an eighth note d and an eighth rest
Lesson 20: #105 - measure 7 in the bottom soprano part should be quarter note a instead of b