In an ideal world, our lessons are not interrupted. In the real world...
And in the real world, the teacher must know how to deal with them.
It is unprofessional to take teaching time - for which a student is paying - and use it for personal activities. Nor is it acceptable to take one student's time and use it for another's benefit.
Be sure to notify your family members and close friends that you now have a machine and ask them to leave a message because you won't be able to answer the phone during teaching time. Some people do not like "talking to a machine," so ask them please to call back after your teaching session. Give them a safe time to call back, such as after 8:00 PM (after the family has had dinner, the toddlers have been bathed, etc.).
Do not let your children take messages. Fifty percent of them will be scrambled, incomplete, totally incorrect, or not delivered. Particularly if you are advertising for new students, you don't want to miss a single call that is an inquiry about lessons.
Messages from current families are even more important. These should not be missed and should be acted upon immediately. Your current clients deserve even more consideration than possible clients! Putting your child in the loop is a blueprint for disaster and embarrassment.
Remember that the first contact with you and your studio that many people will have is your answering machine (or a child who garbles or forgets to deliver the message).
Pow-wow with your family, especially with children who are home after school, and let them know that the machine is now in place for business reasons and therefore they are -not- to answer the phone. Instead, they should call their friends. (A pager or a cell phone is another a good solution, especially for a teen.) If your machine has a feature which allows you to screen calls by turning the volume up and down on the incoming message, it is your choice whether you allow them to "turn up the volume" so they can see if the call is for them. With older children, another alternative is for them to get a job and pay for their own phone line (or cell phone/pager)!
I also suggest unplugging the bell on your phone. Not only is it a distraction for you and your students, but it also is a powerful temptation to your family members to answer the phone when it keeps ringing.
See this file for a discussion of the greeting message for your answering machine/voicemail.
The first time it occurs, answer and politely explain that your son will be out to play when he's done with his homework. In the future, would the playmate please not ring the bell and instead wait for your child to come outside? That will mean he's ready to play; if he's not out there, it means he still has homework to do. Most kids will oblige you willingly.
If solicitors come to the door, as soon as you see who they are, say, "No, thank you" and politely shut the door, even if the solicitor begins talking.
Neighbors who drop by to "chat" should be told, "I'm teaching right now. May I call you this evening?" In the course of the later conversation, you apologize for "not being able to talk this afternoon" because "from 3:00 to 6:30 every day I'm at the piano." Most adults will get the picture right away.
I feel it is ok for parents to take their -own children's- time, but not other students'. If the parent comes in at the beginning of the lesson, take as much time as you think the topic warrants (certainly not the whole lesson!) and then say something like, "I need to think about how we can solve this problem" and say you'll call them at home in the evening.
If you don't want to spend any lesson time at all talking to the student's parent because you have so much to accomplish that day, I suggest the following: "I think we'll need more than a few minutes to discuss this, and I hate to take that much time from Susie's lesson. May I call you tonight?"
What if the parent wants to talk after the lesson, in what is the next student's time? Obviously, you cannot allow this, even for one or two minutes. Try this: "I'd love to talk now, but it's Jason's turn. Would you like to talk about this first thing next week at Susie's lesson? I'd be happy to do that or you can call me this evening." Smile and look a tad rueful. The parent will get the message.
Don't leave things up in the air but take charge: "If I don't hear from you before then, I'll be ready to talk with you first thing next week. See you all then!" Turn to Jason: "Ok, Jason, let's start with...."
If, at the next lesson, the problem seem to be one of those that will take longer than one or two minutes, conclude the conversation as gracefully as you can with the promise to call the parent that evening.
More on parental interruptions in this file. It also includes discussion of what to do when the parent wants to talk during the lesson (either to tell you about the child's practice during the week or assist you with teaching).