First of all, the amount of time that a student needs to practice differs greatly! Below you will find some general practice guidelines. More is ALWAYS better. :) My personal best was 14 hours straight one day while attending junior high school. I was nuts!

5-6 years old > 5-10+ minutes per day, 3-5 days pers week. (they will usually need your assistance)

7-9 years old > 15-20+ minutes per day, 3-5 days per week. 10-12 years old > 30+ minutes per day, 4-5 days per week. 13 to adult > 40+ minutes per day, 5-6 days per week.

-- Comments welcome!