It is quite normal for a school to block VPN traffic. They block VPN traffic because it is a means of bypassing their filtering completely.  When a school uses no MDM you can download and activate your device with curbi kids.

If your child has an iPhone or iPad that they use at school, curbi will work just fine with it.

Your school does have to register with us in order to have curbi work at the school.  Just send them this link

After the schools registers with us, all you need to do is select the name of the school from the Device tab and then click on "select school".

From Safari:

or from the Parental App