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If you have not created a Parent Portal account, please refer to this article, How do I log into PowerSchool, to find the steps to setup up your account. This is a quick guide: Student and Parent Portal Quick Start Guide to help you access the Parent Portal. The access ID and access ID Password helps link students to your Parent Portal account, it is not the same as your Parent Portal credentials. You will have to set those using the Create Account button on the Parent Portal page.
If you have already created an account, click on the forgot password button to reset your password. The steps mentioned in this article should help, Reset Password.
You can refer to this article: Adding Students to the Parent Portal to add a student to your Parent Portal. In case you 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.