Knowing what practice is and why it is valuable will assist you in helping your student make the most of their time at the instrument. It also will guide you in dealing with the resistance that will happen on occasion, even with the most dedicated person.
Research shows that maximum retention occurs if practice takes place within 24 hours or less. The retention rate is approximately 90% if repetition does not occur until 48 hours later. If you skip a day of practice the retention drops off drastically.
Practicing seven days a week is not realistic for every student or every family. The student will most likely enjoy a day off. If students pracitice six days a week, their tasks will be well-reinforced and "skipping a day" will not affect their over-all retention significantly. The day after or before the lesson is never a good choice for the "day off" day.
Home pracitice is also a time to experiment. After completing an assignement, encourage your student to explore. Perhaps they can pick out a tune by ear, play a song they already know but in a a different way, or make up their own song. Looking ahead in the materials is another productive activity; your student can see how much of the upcoming information they already know and can challenge themsevles to figure out some of the rest.
Finally, home practice is a time for the family to participate in the studen'ts music study. This can take the form of "family concerts" after dinner, or playing duets with another family member.