This is because the Students information is not set to publish to the Teacher Role.
To fix this navigate to:
  1. Core
  2. User/Access
  3. Profile
  4. You will land on the tab Edit User Profile Data
  5. Search the User
  6. Click on the Users Name
  7. Scroll down to System Information
  8. Click on the link "Select information to be published in the online community."
  9. Click Edit in the top right
  10. Select the Items that are not being displayed that should be (Email in this example)
  11. Save
OR
  1. Core > People Finder
  2. Search the User
  3. Click on the Settings tab
  4. Under Privacy Settings "Include my name and only the specific information selected below to those specific constituent types." Select the Teacher Tab
  5. Mark off the items you want the Teacher to see
OR

you can reset the Profile Publish fields for ALL Students to Teachers in case you had a bunch of Students change this. 
Note: Resetting Publish Fields for ALL users will NOT override an individual's selection to "Include my name, but do not include any other information about me." To reset access, the profile fields have to be manually set through the user's individual publish settings.
  1. Core > Settings > Profile>
  2. Select the tab for Profile Publish Access
  3. Leave Student in the dropdown and select Student to Teacher in the Manage Publish Fields link
  4. Select Edit in the upper right
  5. Select the Radio Button for Reset Publish Fields for ALL Users
  6. Click Save and Confirm
  7. Click Confirm
Note: these changes can take 24 hours to refresh, so the change may not take effect immediately.