I'm not a lawyer, but I'll share my personal opinion.
Sunshine laws (open meeting laws) are state regulations that require government agencies and some nonprofit organizations that receive public funding to open at least some of their board meetings to the public.
It could vary state by state, but generally I don't think they would apply for typical PTOs. (And even if they did, you'd have a tough time finding anyone to enforce non-compliance at that level.)
That being said, there are expectations that the organization will follow its bylaws and accepted best practices. Certainly it would be a normal practice to have publicly announced meetings, meetings open to all members, access to minutes, proper notice of elections, etc.
There's a real struggle for balance when you get to issues like open meetings and open records. You don't want critical stakeholders (like parents) excluded from meetings. You don't want official business conducted in the shadows. On the other hand do you want these meetings legally open to the world where you have no power to set limits? What if there's a very controversial group with NO stake in your school simply looking for any public forum in which to cause disruption and state their views? Sure you can try to control the agenda, but in an open meeting, you can't prevent them from participating.
As far as "open records", if it is a 501(c)(3) non profit registered with the IRS, then there are certain pieces of information, like their 990 return, which the organization must supply upon request or face financial penalties from the feds. (I think $20 per day.)
But if it were truly subject to open records requests, the implications could be awesome. Another fundraising group might request the names and contact information of all the PTO's donors so they could save time over collecting their own info. You'd get into issues on what was private versus public information of the members and what could/should legally be released. Once that door is open, it becomes quite complex.
For instance, we had a mom ask for some PTO membership/volunteer records one time because she wanted to use them to help substantiate her ex-husbands' lack of involvement in a custody hearing. (No, we didn't provide them.)
Here's one link that might give you more information:
openmeetinglaws.com/NonProfit.html
