Personally---I can't think of a reason. I have about 3 tiers of plan for just about everything/everyone we do business with--there is a really high end plan that covers just about everything, a upper end plan, a pretty decent plan and one that is "competent" but that is about all.
With the devils advocate hat on
however, the pressure to compete with folks that offer more for their levels than the "other" guy sees a lot people jumping ship....market forces have serious effect here.
When your viewed as little more than a number by the people your doing business with its EASY to quit.
"Should I give the same treatment to the student that comes to every class over the student that only comes occalsioal?"
Do they pay the same per month????
If so, and your following a business model--Yes.
Think of it like this---do you expect to be ill-treated by a store you only shop at every now and then?
Of course not---you have money to spend and you expect to be treated just like everyone else buying bath mats and laundry soap.
"Is it my fault that one student learns faster than another?"
Nope, but as a paid teacher your expected to be able to improve the quality of the student.
If I hire a cleaning company--I may have to pay a little more than the office next door if I generate more mess---but I damn well better be just as clean when they are done.
Its one of the problems with a business model in this kind of situaton---your stuck with whatever the customer brings to the table in ADDITION to what you bring.
You can't be responsible for thier lack of effort-----but but by the same token---if you can't get the job done--then you need to fire them as a customer and return any monies not already spent.
"My time is just a valuable as your time"
Personally I'd agree.
The business model however says that your essentially "selling" them your time....you fixed a price---and your time is LESS valuable than theirs at that price.
As long as that price is being met then no customer is worth more than another (you can play with this one) and/or since they paid for TIME, your required to be there--remember your get paid for that time even if no-one shows up and you spend the hour reading a book or doing Sudoku.
"if I'm not a good teacher, you wont be back next month"
If you have that option---but contracts--not market forces--often force people to keep coming back to "NON-good teachers."
Remember the Devils Advocate hat is on
--are Black Belt Clubs part of "good teaching??"
Or are they essentially social programs to keep people interested in classes they would otherwise quit--REGARDLESS of the quality of instrution?????