In 35 years I have been invited to childrens' soccer games, music recitals, birthday parties, afternoon fishing expeditions, track meets, etc., etc. I have never once myself or seen another teacher invite a student to a political demonstration of any kind.
I don’t think it’s a phenomenon at all in K-12; I think it does occasionally happen in the higher education world.
It isn't a "phenomenon" at any level, Ivan. If a high school or college teacher attends the same demonstration as his or her students, it's by choice, not by invitation.
…once again, the specific thing discussed in this article was an instructor saying they were going to participate in a pro-Palestine demonstration and inviting the students to do the same.