First, I've never heard of this, so though I am not an elementary school teacher, I feel justified in questioning your "75% of schools" figure. Secondly, if this is being done, it is almost certainly happening so that the teachers can supply the children who are too poor to afford their own supplies with the materials necessary to learn. There is an easy fix for that: deal with the funding problems in schools, in whatever way you think appropriate -- raise taxes, audit school spending, reduce administration, or, if you prefer, fire teachers. Or, on a more personal level, go spend $50 on pencils and give them to a local school.
It isn't the best solution, but saying it is an attack on the concept of private property is blatant hyperbole. Tell me, do the teachers also make the children strip and share clothing? Do they refuse to call children by name, preferring "Comrade?"
Trust me: the teachers union can give me all the guidance they want, it doesn't mean I will follow any of their suggestions. My administration has never given me any suggestions of the sorts of things I should teach, or discuss, in class, apart from asking teachers to refrain from cursing, discussing sensitive issues such as birth control and abortion, and other non-offensive guidelines. I have never had a political position of any kind required of me.
Unless you count confiscation of weapons and controlled substances an attack on personal freedoms?