In the following which is correct, and why?
1) I didn't know that you could play the piano.
Oh yes, I have had piano lessons for a year.
2) I didn't know that you could play the piano.
Oh yes, I have been having piano lessons for a year.
An explanation would be welcome. I think both are correct, but I was told only the second one was. In the 1st sentence we know for how long but not when, so why can't one use the simple perfect form ?