Parental Involvement in classrooms

In order to continue my link with education, schools, and students, I inquired in some NJ schools regarding volunteer opportunities. I was looking to be in the classroom with the teacher, helping as an instructional assistant, but only FREE OF COST! I figured with my teaching background and qualifications, I would have no problem and I was also willing to go through a background check. To my surprise, the schools do not have any volunteers in classrooms.

As a former teacher, I was not only provided a teacher's assistant, but I also invited parents to become classroom helpers whenever it was feasible for them. There is so much research that states parental involvement in the classroom not only improves school-home relations, but also improves student achievement.

I was quite shocked that not a single helping hand is available to these teachers. Moreover, a bit disheartening was that I didn't get a response back from a couple of my inquiries.

Why not have parent or other volunteers in classrooms to lend a helping hand??