practice and lesson

In general which is correct?
Does the plural indicate I have more than one lesson at one place or just mean i have the same lesson and teacher on more than one day?
I have piano lesson
I have piano lessons



If I switch lesson to practice
Should practice be plural or not?


I have piano practices on Saturdays
I have piano practices on Saturdays

On the whole, pratice would be singular. I have piano lessons is an all-encompassing title that covers more than one lesson in more than one place with different teachers. To be more specific you would say I have a piano lesson at, with (but it has to have the indefinite article).