If you aren't sure if you have billed your clients for all of the lessons they've scheduled, you can use the Lesson History table to view uninvoiced lessons. You can follow the steps below to view these lessons:
Click on "Calendar" and then click on "Lesson History by Student".
Using the filters at the top-right of the table, select the date range you'd like to use.
Select the "Uninvoiced" option in the second filter.
Click on "Go".
The table will be refreshed with the selected filters and display any lessons that have not been added to an invoice. You can then generate an invoice for the client and pull those lessons onto the invoice.
NOTE: If you invoice students for Packages and not individual lessons, the lessons will not appear as invoiced since they were not added to an invoice. In this case, you can refer to the "Package Balances" table found under "Billing" to view their package usage, or you can use the Uninvoiced Nonpackage Lessons Report.