A Certificate of Good Standing is just a way a state keeps track of businesses and produces revenue for the state(the simple definition), the madated fees are filed yearly and in my state they are $25 a year.
The site will be able to give you info. on if your PTO is registered as a 501 (c)(3), and the current standing, i.e., A= active and in good standing, N= active and not in good standing, etc.
You should also be able to do a search on your state's Secretary of State web site and also find out if your corporation has filed a recent Certificate of Good Standing.