If you are unable to attend one or more of these classes for valid reasons (eg, illness, family emergency, unavoidable transport issues), you should contact your class teacher in advance of or immediately after the class to inform them of the reason for your absence.
Certain absences can be authorised, and more information about these can be found here.
If you fail to communicate the reason for your absence or if this is not for a valid reason, your absence will be considered unauthorised/unapproved.