They know lots of PG kids homeschool and they are supportive of homeschooling, so don't worry. This is not at all an uncommon situation. I'm sure piano teacher would be fine especially if he or she knows him well. We asked a homeschooling co-op teacher who knew our child for just six months and it was fine. As the child gets older certainly it is a good idea to bring in more outside teachers and mentors into their lives.