A question I am often asked by young teachers is, "How long should it take my students to get through each method book?" The short answer is 3 - 9 months. The long answer is, it depends on the family. (You thought I was going to say it depends on the student.)
The average student needs parental help to schedule, maintain, and support their music practice and scholastic homework through the age of eleven years. This is the same for after school athletic activities.
It is interesting to note that athletic coaches realized (about 35 years ago) that parents were no longer encouraging dance and sports routine practice between lessons. Dance studios and soccer coaches took the lead in restructuring private coaching sessions and team classes as a requirement on more than one day a week to be accepted as a student.