Anyone who is planning what they will teach you more than a lesson or two in advance is rationing knowledge and not responding to your progress. A teacher who was responding to your progress would barely be able to plan through to the end of the lesson from the start, because how far you will get depends entirely on how quickly you master what they start the session with.

If they are going to teach you according to a fixed schedule, you might as well take only group classes - the whole point of private lessons is that they move at your pace.

This is just another example which demonstrates most chains are more focused on selling you lessons than teaching you to dance. The argument that you need to make a committment to them doesn't hold water when you see all the amazing amatuer students coming out of independents who never signed a contract. If a student geniunely enjoys dancing, and their teacher is top notch, the student will see improvement and continue with lessons....it's a self perpetuating process.