At our school we have a cut off date for the faculty to join. If they join by that date they can turn in a receipt for up to $50 in supplies (this must be a clean receipt) and we reimburse them. Our fee is half of what it cost a family to join. We have always had 100% participation. This year as an added incentive if we reach our goal of 900 members each class will get an additional $25 gift card to use toward their class.
Our organization decided to waive dues for all teachers and staff. They are automatic members and don't even fill out the membership form.
However, in our annual membership drive - where the top three classes get a prize - if a teacher is also a parent, they DO need to fill out the membership form in order for it to count towards their child's class. (But they still don't pay dues.)
We have teachers join our PTA just like the familes do. They fill out a form, pay dues and get a membership card. At our school the Teacher/Staff membership is always 100%, unlike the familes!!! We never have a problem getting staff to join, but every year it seems our Family membership goes down.