I am a private piano teacher who teaches out of my home. I have recently gone back to teaching 3 days a week (for 3 hours) and have arranged for a friend to take care of my 3 month old while I teach. I was all set up with bottles of expressed milk, but he has been refusing to feed with my friend. Do you think it would be appropriate to nurse him while I teach a lesson occasionally?
Unfortunately, some people are just ignorant in this world and will take offense to a mother feeding her child. There are many who would not find it a problem in the least. Some who will suggest you cover yourself and the babe with a blanket will be their solution. Some won’t like paying your time for feeding your child. They’ll think it’s somehow taking time away from their child and the lesson.
See why i used the word ignorant in there? 
You breast feeding your child gives your child a boost up in so many ways. It’s natural and should be done for every child. Sadly, too many have hang ups, or are too selfish to bother. They bring every excuse in the book they can.
You’re best bet, try to start working the child into a schedule where they it doesn’t need to feed during that particular time frame. 3 hours isn’t too long to go without feeding at 3 months of age. You could also schedule a 15 minute time difference inbetween one lesson if truly need by. Giving you enough time to feed the child while no one is at the house.
Personally, i would find it totally appropriate to nurse your child around me. But i nursed as well.