If I connect my existing CommonLit account to Clever, will my assignments and data disappear?

No, connecting your CommonLit account with your Clever account should not delete any previous data. However, you may wind up with duplicate copies of your classes, as it is not possible at this time to merge existing classes with new Clever classes. Your old classes and their data will remain unchanged though. 

This video will walk you through how to safely match your CommonLit and Clever student accounts: