Why is the attendance icon "@" not appearing on class

Teacher's timetables:

• The teacher is not in a permission group with the permission 'ATT:EDIT'. To resolve this, complete step two in the article Setting Up New Staff Accounts
• The class is a Calendar class and the 'Allow Attendance' option is not selected. Click on the edit icon on the class and if required select Allow Attendance and click 'Save'
• The class is an Untimetabled class. Untimetabled classes are not associated with a period of time. As such they cannot be used for roll marking.