Have you added the Tutor to the Cohort/group that the students are in?
If you log in as the System Administrator, then go to Manage Cohorts in the left hand menu, then edit the cohort/group you are wanting to add the Tutor to. Under the orange bar, there will be a blue box with Manage Users. Click this button and it will list all the users on the system. Tick the box next to the tutor to add the user to the cohort/group. There will then be a green box at the top confirming that the user has been added to the cohort/group.
When you log in as the Tutor, they should then be able to see all the students in that cohort/group.
This is explained in the Help Centre guides under the following link: https://myknowledgemap.zendesk.com/hc/en-us/articles/201028713-How-do-I-add-users-to-cohorts-groups-
Hope this helps!