Are LEAs or schools required to have written agreements with the CWA or tribal organization prior to disclosing PII from education records to the welfare agency or tribal organization?

No.  The written agreement requirements in the FERPA regulations do not apply to a disclosure of PII from education records made under this particular exception by an LEA or school.  However, LEAs and schools may want to consider a written agreement, data sharing agreement, or memorandum of understanding (MOU) with a CWA or tribal organization to ensure that the CWA or tribal organization is aware of its responsibility under FERPA to protect PII from education records from unauthorized disclosure.