A parent portal only helps if parents use it. The rollout matters more than the feature list: who hears about it, from whom, and what they can do the very first time they sign in.
Before invitations go out
Send invitations in waves
Start with one or two classes whose parents tend to adopt new things quickly. Answer the questions they raise, then invite the rest of the school. A single blast to every family creates a day of phone calls nobody can handle.
Give parents a reason to log in
The first login should answer a real question: what do I owe, and can I pay now? Publish invoices before invitations and parents quickly learn the portal is where the answers are.
Keep the old channel open — briefly
For the first few weeks, accept calls and visits while pointing every question back to the portal. Then set a date after which statements and receipts are issued through the portal only.