Why do you call public school a “union monopoly?” Is you local police force then one too? What most people fail to see is the power they actually hold in their public schools in most places. I can not comment on all states, but I know how it works in mine.
We vote for our local school board. We can attend and speak at school board meetings. We vote on the budget that we have full access to. We have access to decision makers within the administration, including curriculum.
Yes, you can make a difference in your public school.