First of all breakem, many of these groups come under stealth........parents aren't notified that such a group is coming......
Let me see, the country has advance notice of this demo. It's all over the net. Duh! Do we think the kids don't know in advance. And of course if the kids know, the parents would never find out.
If you have a group attacking or sneaking up on your school, may I suggest you form a perimeter around the next board meeting. If you want kids to not be silent, you will not stop them. Only they and their parents can do it. Wake up and smell the coffee.