Hi Julie,
Our project is a labor of love from the Celeste modding community, and we want our music to be as accessible as possible to everyone! The game and it's music are available for free online, and there is no ASCAP copyright associated with this sheet music. This is the official and only store front for the Strawberry Jam Piano Collections, so I would imagine that sharing a link to this download should suffice for your son's piano teacher. If you need further assistance or confirmation, feel free to send us a message at celestestrawberryjam@gmail.com.
~BeanJammin