Students can log in to their ClassDojo accounts using multiple ways, including Google Login.
When using Google Login, teachers must provide the student a Google Signup code, which is a unique 6-character code that allows a student to connect to the teacher's class. The student will first go to "dojo.me" in a browser, tap "Sign in with Google", and then go through the Google steps to log into their Google account and to grant ClassDojo permission to let them sign in and for ClassDojo to access their email address.
If you, as a teacher, choose to allow your students to log in to student accounts on ClassDojo using their Google for Education or other Google Accounts, you are responsible for educating your students on the proper use of their Google Login, including to help educate your students on better protecting their Google Login by turning on two-factor authentication. Note that ClassDojo does not request or store passwords associated with any Google Logins.