In the App Control panel you can not only send a message but you can also identify whether a recipient has opened the message or push notification.
All push notifications that you send are logged in the control panel. Then for each message, you can see to whom each message has been sent and whether each recipient has opened the message.
The notifications are split into a heading which is limited to 140 characters (as Twitter used to be) and a body part which is an unlimited number of characters. As soon as the recipient has opened the main message this registers as a read receipt. Clearly the successful method of identifying whether a parent has opened the message is to send a tempter...i.e. "Important message about the school U15 football team please open....."