Question: I was wondering, how long should a beginner practice?Alanna (California, USA)
Albert's reply: How long to practice piano depends on the student's age. For very young children (around four to six years of age), 15 to 20 minutes of supervised piano practice will suffice. The primary task will be to build the child's capacity for concentrated learning.
At least one parent should attend all lessons with young children and that parent should supervise their children's practice, making sure that all exercises are completed as instructed by the teacher. The goal is for the child to be able to perform independent work at the piano. (At the professional-track level, ideally nearly all practice should be supervised and corrected by a master teacher, but only exceedingly few students have this luxury.)
Teenage and adult beginners should practice at least 30 minutes a day, six days a week. Once you have developed a proper working methodology, a practice regiment of 45 minutes to an hour five to seven days a week should be considered mandatory.
Beginners need to focus most of their effort on developing the many essential skills necessary for playing the piano. Each skill or facet of music—rhythm, reading music, sight singing, music theory—should be practiced separately before attempting to combine them.
Once you've progressed to an intermediate skill level, your next goal should be to maximize your efficiency (see Efficient Piano Practice) to make the most of your practice time and accomplish more with less time (but not less mental effort).
For a proper working methodology that is suitable for early intermediate to professional-level pianists, please read my article How to Learn Music.