Hi!
We found that the teachers in our district were severely undersupported. We were able to work with the existing PTA to just lighten the load and provide some resources. That helped in the moment, and bought us the trust of the teachers, which is really valuable. Frankly, it shouldn't have been necessary, but it was an opportunity to show we were there to help.
I have found in our district that if you can get the ear of school board members or members of administration, they really appreciate keeping feedback private. So, as long as I feel that they are taking issues seriously, I try to respect that. I have walked up to an admin at a public meeting (on the side) and said, "What can we do about x?" She knew that I was there to help not to criticize, and she told me what was actually needed, which I could then go work on.
Also though, we communicate, communicate, communicate as parents. That has helped the leadership understand that we are not "just that mom" and that they need to take any of us seriously when we bring up issues that we see.
Finally, you have to separate advocacy to change the district from advacocy for your child. It might be the legal aspect, I'm not sure, but administration will always clam up if it's about your child. You need to make it abstract in order for them to engage, at least that's very consistently been my experience.
Best wishes on your meeting!