If you at any point expect to transition between billing students using the "Package" billing method to another billing method, the it's important to understand how packages are tracked.
When you invoice a student for a package of lessons you will need to select the service type for that package. When you schedule lessons with the same service type, they will be deducted from the student's package balance for that service.
However, if you decide to switch to billing the student per session for the same service, those lessons will continue to be deducted from the package. The opposite occurs if you bill a student per session and then begin billing them for a package with the same service type, when you record the package all of the lessons with the same service from prior to the package will still be deducted from the package.
The solution is to create a separate service type for any service that you bill by package or using a different billing method.
For example, if you have a service called "Math Tutoring" you would add a service called "Math Tutoring - Package". When you record a package you would select the "Package" version of the service and when you schedule lessons for the student you would also select the "Package" service. If you ever switch to billing the student using a different method, then you can use the standard service type.
Another solution is to archive the package. When selecting an "Archive Date", any lessons on or before this date will be excluded from the Package Balances table. If additional packages are purchased and subsequent lessons are scheduled after the date, these will be tracked in the Package Balances table. For more information, please see this article: How to Archive Packages