I never thought of not charging dues. For membership in the middle school PTO we charge $10. With approximately 270 members we take in $2700. We send them a pocket size version of the school calendar in return.
I don't think that paying for membership is necessarily a deterrent to people joining.
I think people believe that if they join the PTO they will be expected to volunteer.
I've also seen people believe they can't volunteer if they are not a member.
The elementary schools have many events that require help and perhaps people think the same amount of help is needed in the Middle School and perhaps that discourages them from joining.
I would consider decreasing the cost of membership or perhaps offer it for free in an attempt to increase membership.
One of the main advantages to joining is that it gets their email address on the PTO list and therefore enables them to receive information on a regular basis from the PTO.
I could see dropping the fee and have a large membership push. On the form there could be a tear-off form inviting people to make a contribution to the PTO.
The priority is involvement and educating the parents about the PTO. If we can improve both then we are more likely to get members on a consistent basis.

I love Marci's idea of tying donations to a special deal at the book fair. How about this: Take that one step further and give the parents a flyer they can send to relatives, especially ones who live out of town. What an easy way for them to get Christmas presents for your kids, and they can help raise money for the school as well. How many times have your kids gotten a gift they hate from a well-meaning but clueless relative?

I guess I'm so new to this PTO business that I would have never, ever thought a PTO would charge dues. I've been involved with the PTO of my second-grader's school for two years and attend every meeting I can (I also do the thrice-a-year PTO parent newsletter). We're lucky to get a dozen parents to attend the meetings, but we just raised $18,000 during our fall fundraiser. Our parents step up when needed and instead of being nickel-and-dimed for dues, they help in larger ways. I just can't see the purpose of dues.

Actually, we don't charge dues. In our opening letter we let everyone know that anyone with a child in the school is considered a member of the group. We let them know when all the meetings are and what is on the agenda for that month and let everyone know they are welcome to attend at any time. We always felt that the little money we would raise would do more harm to getting people involved than it would help financially. And the more people we have involved actually raises the participation at our fundraising events, which I am sure has more than made up for not charging dues.

We call it a "Pledge Drive" and we raise a great amount of money! We tie the donations to the Book Fair held right after our drive in this manner: "Pledge $25 and get $15 worth of FREE books at the Book Fair!" Our elementary school makes well over $2,100 and we are in a very moderate/low income neighborhood. Couple that with our decision NOT to start the year off with a fundraiser, and it was tremendously successful. We likewise have "donations" of $5 and $10, but gladly take any gift. Hope that helps!

We don't charge dues to be a member, but in order to be voting member, you must pay $3.00 per family, per year and attend at least 2 meetings (they don't have to be that year or consecutive). This keeps members from recruiting one-time attendees to come and push through or vote down a contested issue. We have many members who don't pay the dues because they aren't worried about setting policies or making decisions. We also have many members who don't attend any meetings or vote, but are there for every volunteer opportunity. We are involved in the 4 schools K - 8 in our district and I care a lot more about having a volunteer than having their $3.00.