Students are unable to share their screens during a live lesson on Microsoft Classroom due to the teacher’s account settings.
In order to fix this situation, a few measures should be taken:

1. Ensure the correct account settings are enabled on the teacher’s account.
2. Verify that the teacher has given permission for the students to share their screens.
3. Test if the students can share their screens outside of the virtual classroom.
4. Check if the students meet the minimum hardware requirements.
5. Ensure that the new group of teachers and students have given the teacher the necessary permissions.

If these measures are taken, the student should be able to share their screens during the lesson.