I have never done it before and someone may come along and give you really helpful information.
But to my way of thinking your best bet may be to disband the entire organization and create a new one that is solely for the elementary school.

Perhaps doing this will also make some of the parents in the other schools get off their butts and do something!

We are the PTO in a small town. The most involvement comes from our 2 Elementary's (Pre-k - 1st, 2nd-5th). We were wondering if there were rules or bylaws to follow to dissolve the Middle School and High School from our PTO. We have NO parental or school involvement from either, yet give to both of them. Even scholarships to the High School. It's frustrating for us to tell the Elementary we can't give them money for their covered walkway because of something at the High School when they are the ones that participate in our fund raisers! We can't get the middle or high schools to even participate in those!! We know in a couple of years our children will be at those schools and we could possibly start up one then with, hopefully, better involvement. Has anyone else had this problem?? Thanks in advance