Just do the exact below steps:

1. Connect your device to your PC/Mac

2. Open iTunes

3. Select your device

4. Tap "Apps" or "Applications"

5. Scroll down to "File Sharing" section

6. Select TeacherKit

7. Delete the file called "LOCK_ENABLED"

8. Double tap on your home screen and terminate the app

9. Open the app again and you will enter normally