Thanks for reaching out!
For students to properly sign into the accounts that appear in your section, they need to make sure they are always signing in using the “continue with Google” option (red button) on the far right side of the sign-in page (studio.code.org/users/sign_in). Having lessons assigned to Google Classroom will not ensure they log in automatically via this method; students need to proactively choose this method upon signing into Code.org for their progress to be saved in a place where you can view it. We are working on updates to this assign-via-Google-Classroom method to force a sign-in (through the correct method!) to alleviate this issue, which has been reported by other classrooms recently.
Students signing in with any other method, such as typing their credentials on the left side, will result in them being signed into some other account, other than what you have set up for them. We also don’t require students to sign into the site at all to use most courses of ours, so signing in via the proper method is essential for both their progress to be saved and for you as the teacher to view it.
Hope this info helps!