And....... if someone or a group of people take off on a discussion not on the agenda, you may call for "Orders of the Day". This is a privileged motion that takes precedence over any and all other motions of any other type listed before it. Orders of the Day require the assembly to immediately return to the agenda/schedule topics.
Do you have a section on your agenda for "new business"? When I was PTO pres, I would place that item toward the end of the meeting so that if someone had something to share, there was time.
But certainly, if someone comes to you and asks for time at the meeting to discuss something that is of interest to the entire membership, you could put them on the agenda and provide them floor time. Just make sure to vet the topic carefully---one of my biggest mistakes as PTO president was allowing two individuals--one parent and one teacher--an agenda item and floor time to discuss fundraisers that were personal to them but were of no real interest to other members--in fact, I got a couple of late night calls on one person's "presentation" because she really came off as "pushy". Think carefully about how much your membership's time should be spent on listening to a pleas for help with a society walk or a raffle that has no real impact on your organization. Families are already feeling tapped out, and having someone with their hand out is more stressful to them.
The same goes for concerns that are limited to one group or one individual. It's one thing to discuss an issue that has raised school-wide concern--for example, th quality of school lunches or sports funding. But if it's limited to a particular class---say an issue with 1st grade--then that person should be encouraged to discuss it with the appropriate parties. I also had a no personal attacks rule. Yes, the meetings were called "boring" by some who thrived on it from years past, but going at a teacher or another parent just for sport in a meeting was always a no-go. In fact, I had some parents who to this day hate me because they went at the principal during a meeting about the dismissal of a teacher and my husband (co-pres) and I put a fast end to it. It wasn't appropriate discussion (it was a personnel issue--none of anyone's business) and the attack was unwarranted.
There's a place and time for everything--especially when it comes to PTO meetings.