If you wish to not receive the lesson and test completion emails, you can turn them off with an account-level setting.
Login with your parent/teacher account and find the "Hello [email]!" in the main menu. Click on that menu item and you will be taken to a page where you can manage your email/password. You will also see a setting for Emails where you can turn on/off the Lesson Complete Emails by clicking the link. It will automatically save the new setting after you click the link.