All parents registering to join any school's Classlist site must first be approved, in order to make sure that all the members of the site are genuinely part of the relevant school community. You cannot join a school's Classlist unless you have a child attending that school.
Approvals are done by existing members of the site with the necessary level of administrative rights - usually a parent Ambassador or Class Admin, or a member of staff at the school who is registered as a Staff Admin. These admin account members will typically be people who are already involved in the PTA or school community, whose identity has been confirmed by Classlist's central team when the school was first registered.
The approval process is generally done very quickly, involving basic checks of contact details and confirming that the parent applying has a child registered at the school.
Classlist offers plenty of support and advice to those involved in the approval process to ensure that it is done in a safe, secure and efficient manner.