Once the 'Root level access' permission has been changed for teachers (see District Accounts - Limit Teacher Access)
Teachers now need to be assigned as administrators to the specific groups you (as the district level admin) would like them to access.
Assign a teacher as an administrator of a school group
First sign in to your organization account.
Then hover over, or tap on the group you would like to give the teacher administrator access to, then click on the 3 dot ellipsis that appears.
Click on 'Properties' on the menu that appears
Click on the administrators tab:
Click on "Add admin"
Type the name or email address of the teacher you want to grant access to, then select the teacher's account from the drop-down list.
Then press 'Add'
The teacher will be added as an administrator of the group:
When the teacher next logs in they will be able to see the 'Example School 2' group, and any users that are in this group.
They will also be able to add new students directly to this group within the organization account. Additionally, they can create subgroups (e.g., for different classes within their school) beneath this group.
NB.
If you wish to remove administrator access click on the trash can icon next to the entry for the teacher