I rarely tell my students to practice piano. I do however encourage them to play piano.
Another reason I'm not so fond of the term practice is because it implies that the music you create during that time is somehow less valid, less real, than music you create in exams or performances. A teacher of mine recommended an excellent book on improvisation and in it (ironically in a chapter entitled Practice) Stephen Nachmanovitch writes:
"We think of practice as an activity done in a special context to prepare for performance or the 'real thing'. But if we split practice from the real thing, neither one of them will be very real"
Of course self-discipline is important if you want to reach certain goals with your playing, but I think what's important to keep in mind is that you can, and should, be engaging with and enjoying each step in the process rather than mindlessly toiling towards an abstract end point at which point the real music will begin.
Recently I was delighted to hear a parent of two children I teach piano to say:
"Ríona's approach to teaching piano is fun and pressure free. My two children are steadily progressing at their own pace playing current music they love and are discovering classics when they're ready. Music is played all the time in our house and it's not even called practicing".
I'm currently taking bookings for a month long singing and/or piano course for the month of August. It's a great chance to try out lessons without having to commit to a full semester. For more info get in touch at firstname.lastname@example.org.