I suspect it may be an issue of edit privileges of the user.
Edit features provides an overview of editing features in ArcGIS Online(AGOL).
Some maps include feature layers that can be edited by anyone viewing the map. These editable layers are useful when the map author wants community input. For example, an author might include an editable feature layer that allows the birding community to post their bird sightings directly on the map and attach media files, such as photographs, audio files, and video files, to the specific observation points. Because these features are part of the layer, any changes made on the map are immediately viewable to everybody who has access to the layer, even when the layer is part of a different map. Authors can enable editing on ArcGIS Server feature service layers and hosted feature layers.
You should have full control and privileges to provide access for your students.
The owner of an editable features layer decides whether to allow editing and sets an editing level. Editing levels determine if you can add features only, update feature attributes only, or add, update, and delete features. If the feature layer is editable and you have privileges to edit features, you will see the Edit button at the top of Map Viewer. Edits are automatically saved to the layer.
You could learn more about privileges available to assign to users:
Levels, roles, and privileges
Organizations can use, create, and share a wide range of geographic content, including maps, scenes, apps, layers, and analytics. The ability of individual organization members to access and work with content in different ways depends on the privileges they have in the organization. Levels allow organizations to control the scope of privileges that can be assigned to members through roles.