Your TeacherKit data is saved locally on your device. TeacherKit doesn't store your data on the cloud.
TeacherKit doesn't delete your data in case you update it from a previous version.
If you installed TeacherKit freshly from the AppStore after updating your iOS, TeacherKit starts fresh as it doesn't keep your data in the cloud.
In case you have Dropbox backups, you can retrieve your data from it: