I must confess that I have volunteered at school every single day for a couple years. I have four children in the same elementary school, so one day for each teacher (it was never a full day, usually just a couple hours in the morning) was Monday through Thursday, and there was usually something going on on Friday's that required volunteers, so five days a week. It was no big deal for me to do it, it made the teachers' jobs easier, and the kids are fine with me being there. It was a win-win-win.
Last year, my older kids teachers did not need help very often, but an office worker's mother passed away and she needed an extended time off. I was available to fill in in the office answering phones, doing whatever needed to be done. I was glad to be able to help.
I do volunteer a lot. I do it for my children--taking care of menial tasks for teachers means that they have more time to teach! BUT I have never spoken about things I see or hear in the classrooms or the office. I have even offered to sign a confidentiality agreement. I don't hang out to see my children--they are happy and secure. Many days, I never even saw them.
To me, if you are a volunteer at a school, you should be held to the same high standards as the teachers and staff.