I wanted to tell everyone who teaches that there is a wonderful book specifically for teaching a student to read lines and spaces. It’s a French solfege book called Manuel Pratique pour l’etude des clés (Practical guide for the study of clefs). It’s by Georges Dandelot and is published by Max Eschig. You can find it on line.
With each clef, he starts with an exercise that just has C’s and G’s, and the student practices learning those. Then, in following exercises, he adds the notes that are next to, above and below, the C’s and G’s, and continues on like that. It’s organized, and it prevents the student from inventing some hairbrained way of calculating or counting up or down to figure out the note. If you have a student who doesn’t read music, or is having a hard time, this book is wonderful. Spending maybe 3 or 4 minutes of each lesson with this book will do wonders.