Every student in your school is associated with one or more adult guardians. These Guardians have various permissions for interacting with the Student. Some are permitted to pickup while others may only be emergency contacts. For every student there must always be one Guardian designated as the PRIMARY GUARDIAN.
Primary Guardians are by definition the primary contact for a particular student and are also FINANCIALLY responsible for that student's charges.
Usually the Primary Guardian is the adult who first enrolled the child and who signed the paperwork and/or contract.