We bought a keyboard about two years ago. When I was really young, I had quite a few piano lessons and I can still read music although I like the easy versions. But, my husband had never learned how to play the piano.
He was curious. I have to say that I don't have the experience teaching an adult music lessons. I have taught my brothers a little when I was living at home, which was almost 30 years ago. So I went to the music store in our area (it has now moved back to Reno so I don't remember the name, but you could probably find this series of books in any music store), and asked for a good piano course for adults.
I was shepherded to the Alfred's Basic Adult Piano Course - Level 1. Yes, I was curious. I looked through the course to see if I liked the information. It looked OK to me. So I gave it to the husband. He seemed to enjoy picking through the book. He found middle C by reading it.
Unfortunately, he has not continued with the series, but sometimes he pulls it out and tinkers on the keyboard. Not a bad thing.
Oh well, the keyboard was bought for my pleasure. I still enjoy playing Christmas carols, hymns, and a few rock songs. When I get tired of my selection, I look at his piano course. It has been a good refresher for me, too.