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The parents can refer to this article, How do I log into PowerSchool, to setup up the Parent Portal account. You can share this quick guide: Student and Parent Portal Quick Start Guide to help them access the Parent Portal.
The unique access ID and Password help link students to the Parent Portal account and is provided by the district. It is not the same as the Parent Portal credentials. The parents will have to set those using the Create Account button on the Parent Portal page. They can also refer to this article: Adding Students to the Parent Portal to add a student to your Parent Portal.
In case the parents are using the PowerSchool SIS Mobile App, this article: Using-the-PowerSchool-Mobile-App, should guide them on the process to link the Parent portal.