Under the Individuals with Disabilities Education Act (IDEA), the school must give parents written notice prior to making changes to a student’s special education identification, evaluation or placement, or when it refuses to make changes. This is called Prior Written Notice (PWN).
But the PWN actually comes after the decision has been made to make a change or not make a change. The word “prior” often creates confusion. So it would be typical for parents to receive a PWN following an evaluation or an IEP meeting, not before.
The PWN must include detail about the action that the school is proposing or refusing and the reasons for the action.
This Understood article gives a good explanation.