Should you teach bi-weekly lessons?
My succinct advice: no. You'll regret it.
Generally, bi-weekly lessons are requested by adults who (1) want to get piano instruction for half-price; or (2) don't [think they] have time to practice enough to make a weekly lesson feasible (read: worth it). On the phone, however, they'll state the second reason. Your response: "I understand. In this case, I recommend that you don't start piano lessons until you feel you have time to devote to home practice. I recommend 30 minutes a day; if you don't have this much time, then you'd be very frustrated with your slow progress." You go on to talk to the prospect and ask about goals, etc. If the student still does not have time, you say, "I'll keep my notes on our conversation. I hope you'll call back when your schedule lightens up a little." It's a win-win, and lots of times the adult will call back in a month or so, having shifted priorities and rethought the finances. Or, the prospect could have found some teacher who was willing to teach bi-weekly lessons.
If you do teach bi-weekly lessons despite my counsel, I have two recommendations. These are the result of bitter experience (mine!).
Charge a special bi-weekly fee. This should be 80% of the hourly fee for a *half*-hour lesson (ex.: $30 for an hour, $15 for a half-hour, and $24 for a bi-weekly half-hour). This will give you something extra for your trouble; and there will be plenty. Usually it's that the student will not practice very hard because she's not going to be called to account "this week" and says she'll do better "next week" but never does because practice is not integrated into her daily schedule. For you: What will you do with that empty slot on alternate weeks? How will you deal with slow progress and the frustration this student will feel because of the bi-weekly schedule? How will you go about correcting errors that have been ingrained by two weeks' worth of practice instead of only one?
With a special bi-weekly fee, generally the student will see that for not a lot more, he can have weekly lessons and the better progress this will mean. In our example here, two bi-weekly lessons a month would cost $48. Four half-hour lessons a month would be $60; for $12 more (half the cost of a bi-weekly lesson), that student could receive twice as many lessons a month! Don't mention this, of course, as it will be perceived as hard sell. Rather, let the student notice the financial paradox on his own.
Do, however, make sure your student -knows- that for the privilege of a bi-weekly lesson, he is being charged a higher half-hour lesson.
Also, I strongly advise you to require that bi-weekly lessons be *no make up* lessons. Your schedule is going to be topsy-turvy as it is, so don't allow this student to change lessons to another week, double up another week, etc. If the bi-weekly student can't make the appointment, it's a forfeit and you still get paid. Period.
Make sure the prospective bi-weekly student knows that this is your rule for bi-weekly lessons and that you will not change it, even for sickness.
In short, the bi-weekly student needs to understand that this is a situation outside the norm and there are special rules that go with it. If he's unwilling to accept them, he can become a "normal" student or find another person to teach him.